Added ability for doublemodel to evaluate math expressions using exp4j, fixed typeover issue and made the doublemodel more robust to incorrect input.

core/src/net/sf/openrocket/gui/SpinnerEditor.java

@@ -1,6 +1,8 @@
 package net.sf.openrocket.gui;
 
 import javax.swing.JSpinner;
+import javax.swing.text.DefaultFormatter;
+import javax.swing.text.DefaultFormatterFactory;
 
 /**
  * Editable editor for a JSpinner.  Simply uses JSpinner.DefaultEditor, which has been made
@@ -16,6 +18,10 @@ public class SpinnerEditor extends JSpinner.DefaultEditor {
 		super(spinner);
 		//super(spinner,"0.0##");
 		getTextField().setEditable(true);
+		
+		DefaultFormatterFactory dff = (DefaultFormatterFactory) getTextField().getFormatterFactory();
+		DefaultFormatter formatter = (DefaultFormatter) dff.getDefaultFormatter();
+		formatter.setOverwriteMode(false);
 	}
 
 }

core/src/net/sf/openrocket/gui/adaptors/DoubleModel.java

@@ -23,13 +23,16 @@ import net.sf.openrocket.unit.Unit;
 import net.sf.openrocket.unit.UnitGroup;
 import net.sf.openrocket.util.BugException;
 import net.sf.openrocket.util.ChangeSource;
-import net.sf.openrocket.util.FractionUtil;
 import net.sf.openrocket.util.Invalidatable;
 import net.sf.openrocket.util.Invalidator;
 import net.sf.openrocket.util.MathUtil;
 import net.sf.openrocket.util.MemoryManagement;
 import net.sf.openrocket.util.Reflection;
 import net.sf.openrocket.util.StateChangeListener;
+import net.sf.openrocket.util.exp4j.Calculable;
+import net.sf.openrocket.util.exp4j.ExpressionBuilder;
+import net.sf.openrocket.util.exp4j.UnknownFunctionException;
+import net.sf.openrocket.util.exp4j.UnparsableExpressionException;
 
 
 /**
@@ -55,8 +58,11 @@ public class DoubleModel implements StateChangeListener, ChangeSource, Invalidat
 	//////////// JSpinner Model ////////////
 
 	/**
-	 * Model suitable for JSpinner using JSpinner.NumberEditor.  It extends SpinnerNumberModel
+	 * Model suitable for JSpinner. 
+	 * Note: Previously used using JSpinner.NumberEditor and extended SpinnerNumberModel
 	 * to be compatible with the NumberEditor, but only has the necessary methods defined.
+	 * This is still the design, but now extends AbstractSpinnerModel to allow other characters
+	 * to be entered so that fractional units and expressions can be used.
 	 */
 	public class ValueSpinnerModel extends AbstractSpinnerModel implements Invalidatable {
 
@@ -73,26 +79,46 @@ public class DoubleModel implements StateChangeListener, ChangeSource, Invalidat
 						" value=" + value + ", currently firing events");
 				return;
 			}
-			Number num = 0;
+			
+			Number num = Double.NaN;
+			
+			// Set num if possible
 			if ( value instanceof Number ) {
 				num = (Number)value;
-			} else if ( value instanceof String ) {
+			}
+			else if ( value instanceof String ) {
 				try {
 					String newValString = (String)value;
-					num = FractionUtil.parseFraction(newValString);
-				}
-				catch ( java.lang.NumberFormatException nfex ) {
-					num = 0.0d;
+					ExpressionBuilder builder=new ExpressionBuilder(newValString);
+					Calculable calc=builder.build();
+					num = calc.calculate();
 				}
+				catch ( java.lang.NumberFormatException e ) {
+				} catch (UnknownFunctionException e) {
+				} catch (UnparsableExpressionException e) {
+				} catch (java.util.EmptyStackException e) {
+				} 
 			}
 
-			double newValue = num.doubleValue();
-			double converted = currentUnit.fromUnit(newValue);
-
-			log.user("SpinnerModel setValue called for " + DoubleModel.this.toString() + " newValue=" + newValue +
-					" converted=" + converted);
-			DoubleModel.this.setValue(converted);
-
+			// Update the doublemodel with the new number or return to the last number if not possible
+			if ( ((Double)num).isNaN() ) { 
+				DoubleModel.this.setValue( lastValue );
+				log.user("SpinnerModel could not set value for " + DoubleModel.this.toString() + ". Could not convert " + value.toString());
+			} 
+			else {			
+				double newValue = num.doubleValue();
+				double converted = currentUnit.fromUnit(newValue);
+	
+				log.user("SpinnerModel setValue called for " + DoubleModel.this.toString() + " newValue=" + newValue +
+						" converted=" + converted);
+				DoubleModel.this.setValue(converted);
+			}
+			
+			// Force a refresh if text doesn't match up exactly with the stored value
+			if ( ! ((Double)lastValue).toString().equals( this.getValue().toString() ) )  {
+				DoubleModel.this.fireStateChanged();
+				log.debug("SpinnerModel "+DoubleModel.this.toString()+" refresh forced because string did not match actual value.");
+			}
 		}
 
 		@Override

core/src/net/sf/openrocket/gui/dialogs/AboutDialog.java

@@ -43,7 +43,8 @@ public class AboutDialog extends JDialog {
 			"<b>OpenRocket utilizes the following libraries:</b><br><br>" +
 			"MiG Layout (http://www.miglayout.com/)<br>" +
 			"JFreeChart (http://www.jfree.org/jfreechart/)<br>" +
-			"iText (http://www.itextpdf.com/)";
+			"iText (http://www.itextpdf.com/)<br>" +
+			"exp4j (http://projects.congrace.de/exp4j/index.html)";
 	
 	
 	public AboutDialog(JFrame parent) {

core/src/net/sf/openrocket/unit/FractionalUnit.java

@@ -170,7 +170,7 @@ public class FractionalUnit extends Unit {
 		} else if (intPart == 0.0 ){
 			return intFormat.format(sign*frac) + "/" + intFormat.format(fracBase);
 		} else {
-			return intFormat.format(sign*intPart) + " " + intFormat.format(frac) + "/" + intFormat.format(fracBase);
+			return intFormat.format(sign*intPart) + " + " + intFormat.format(frac) + "/" + intFormat.format(fracBase);
 		}
 
 	}

core/src/net/sf/openrocket/util/exp4j/AbstractExpression.java

@@ -0,0 +1,85 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.text.NumberFormat;
+import java.util.List;
+
+/**
+ * Abstract base class for mathematical expressions
+ * 
+ * @author fas@congrace.de
+ */
+abstract class AbstractExpression {
+	private final String expression;
+	private final Token[] tokens;
+	private final String[] variableNames;
+	private final NumberFormat numberFormat = NumberFormat.getInstance();
+
+	/**
+	 * Construct a new {@link AbstractExpression}
+	 * 
+	 * @param expression
+	 *            the mathematical expression to be used
+	 * @param tokens
+	 *            the {@link Token}s in the expression
+	 * @param variableNames
+	 *            an array of variable names which are used in the expression
+	 */
+	AbstractExpression(String expression, Token[] tokens, String[] variableNames) {
+		this.expression = expression;
+		this.tokens = tokens;
+		this.variableNames = variableNames;
+	}
+
+	/**
+	 * get the mathematical expression {@link String}
+	 * 
+	 * @return the expression
+	 */
+	public String getExpression() {
+		return expression;
+	}
+
+	/**
+	 * get the used {@link NumberFormat}
+	 * 
+	 * @return the used {@link NumberFormat}
+	 */
+	public NumberFormat getNumberFormat() {
+		return numberFormat;
+	}
+
+	/**
+	 * get the {@link Token}s
+	 * 
+	 * @return the array of {@link Token}s
+	 */
+	Token[] getTokens() {
+		return tokens;
+	}
+
+	/**
+	 * get the variable names
+	 * 
+	 * @return the {@link List} of variable names
+	 */
+	String[] getVariableNames() {
+		return variableNames;
+	}
+
+}

core/src/net/sf/openrocket/util/exp4j/Calculable.java

@@ -0,0 +1,33 @@
+package net.sf.openrocket.util.exp4j;
+
+/**
+ * This is the basic result class of the exp4j {@link ExpressionBuilder}
+ * 
+ * @author ruckus
+ * 
+ */
+public interface Calculable {
+	/**
+	 * calculate the result of the expression
+	 * 
+	 * @return the result of the calculation
+	 */
+	public double calculate();
+
+	/**
+	 * return the expression in reverse polish postfix notation
+	 * 
+	 * @return the expression used to construct this {@link Calculable}
+	 */
+	public String getExpression();
+
+	/**
+	 * set a variable value for the calculation
+	 * 
+	 * @param name
+	 *            the variable name
+	 * @param value
+	 *            the value of the variable
+	 */
+	public void setVariable(String name, double value);
+}

core/src/net/sf/openrocket/util/exp4j/CalculationToken.java

@@ -0,0 +1,30 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Map;
+import java.util.Stack;
+
+abstract class CalculationToken extends Token {
+
+	CalculationToken(String value) {
+		super(value);
+	}
+
+	abstract void mutateStackForCalculation(Stack<Double> stack, Map<String, Double> variableValues);
+
+}

core/src/net/sf/openrocket/util/exp4j/CommandlineInterpreter.java

@@ -0,0 +1,58 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+/**
+ * Simple commandline interpreter for mathematical expressions the interpreter
+ * takes a mathematical expressions as a {@link String} argument, evaluates it
+ * and prints out the result.
+ * 
+ * 
+ * <pre>
+ * java de.congrace.exp4j.CommandlineInterpreter "2 * log(2.2223) - ((2-3.221) * 14.232^2)"
+ * > 248.91042049521056
+ * </pre>
+ * 
+ * @author fas@congrace.de
+ * 
+ */
+public class CommandlineInterpreter {
+	private static void calculateExpression(String string) {
+		try {
+			final PostfixExpression pe = PostfixExpression.fromInfix(string);
+			System.out.println(pe.calculate());
+		} catch (UnparsableExpressionException e) {
+			e.printStackTrace();
+		} catch (UnknownFunctionException e) {
+			e.printStackTrace();
+		}
+	}
+
+	public static void main(String[] args) {
+		if (args.length != 1) {
+			printUsage();
+		} else {
+			calculateExpression(args[0]);
+		}
+	}
+
+	private static void printUsage() {
+		final StringBuilder usage = new StringBuilder();
+		usage.append("Commandline Expression Parser\n\n").append("Example: ").append("\n").append("java -jar exp4j.jar \"2.12 * log(23) * (12 - 4)\"\n\n")
+				.append("written by fas@congrace.de");
+		System.err.println(usage.toString());
+	}
+}

core/src/net/sf/openrocket/util/exp4j/CustomFunction.java

@@ -0,0 +1,84 @@
+package net.sf.openrocket.util.exp4j;
+import java.util.Map;
+import java.util.Stack;
+
+import net.sf.openrocket.util.exp4j.FunctionToken.Function;
+
+/**
+ * this classed is used to create custom functions for exp4j<br/>
+ * <br/>
+ * <b>Example</b><br/>
+ * <code><pre>{@code 
+ * CustomFunction fooFunc = new CustomFunction("foo") {
+ * 		public double applyFunction(double value) {
+ * 			return value*Math.E;
+ * 		}
+ * };
+ * double varX=12d;
+ * Calculable calc = new ExpressionBuilder("foo(x)").withCustomFunction(fooFunc).withVariable("x",varX).build();
+ * assertTrue(calc.calculate() == Math.E * varX);
+ * }</pre></code>
+ * 
+ * @author ruckus
+ * 
+ */
+public abstract class CustomFunction extends CalculationToken {
+    private int argc=1;
+
+	/**
+	 * create a new single value input CustomFunction with a set name
+	 * 
+	 * @param value
+	 *            the name of the function (e.g. foo)
+	 */
+	protected CustomFunction(String value) throws InvalidCustomFunctionException{
+		super(value);
+		for (Function f:Function.values()) {
+			if (value.equalsIgnoreCase(f.toString())){
+				throw new InvalidCustomFunctionException(value + " is already reserved as a function name");
+			}
+		}
+	}
+
+    /**
+     * create a new single value input CustomFunction with a set name
+     * 
+     * @param value
+     *            the name of the function (e.g. foo)
+     */
+    protected CustomFunction(String value,int argumentCount) throws InvalidCustomFunctionException{
+        super(value);
+        this.argc=argumentCount;
+        for (Function f:Function.values()) {
+            if (value.equalsIgnoreCase(f.toString())){
+                throw new InvalidCustomFunctionException(value + " is already reserved as a function name");
+            }
+        }
+    }
+
+    /**
+	 * apply the function to a value
+	 * 
+	 * @param values
+	 *            the values to which the function should be applied.
+	 * @return the function value
+	 */
+	public abstract double applyFunction(double[] values);
+
+    @Override
+	void mutateStackForCalculation(Stack<Double> stack, Map<String, Double> variableValues) {
+	    double[] args=new double[argc];
+	    for (int i=0;i<argc;i++) {
+	        args[i]=stack.pop();
+	    }
+		stack.push(this.applyFunction(args));
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		operatorStack.push(this);
+	}
+	public int getArgumentCount() {
+	    return argc;
+	}
+}

core/src/net/sf/openrocket/util/exp4j/ExpressionBuilder.java

@@ -0,0 +1,131 @@
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+/**
+ * This is Builder implementation for the exp4j API used to create a Calculable
+ * instance for the user
+ * 
+ * @author ruckus
+ * 
+ */
+public class ExpressionBuilder {
+	private final Map<String, Double> variables = new LinkedHashMap<String, Double>();
+	private final Set<CustomFunction> customFunctions = new HashSet<CustomFunction>();
+
+	private String expression;
+
+	/**
+	 * Create a new ExpressionBuilder
+	 * 
+	 * @param expression
+	 *            the expression to evaluate
+	 */
+	public ExpressionBuilder(String expression) {
+		this.expression = expression;
+	}
+
+	/**
+	 * build a new {@link Calculable} from the expression using the supplied
+	 * variables
+	 * 
+	 * @return the {@link Calculable} which can be used to evaluate the
+	 *         expression
+	 * @throws UnknownFunctionException
+	 *             when an unrecognized function name is used in the expression
+	 * @throws UnparsableExpressionException
+	 *             if the expression could not be parsed
+	 */
+	public Calculable build() throws UnknownFunctionException, UnparsableExpressionException {
+		if (expression.indexOf('=') == -1 && !variables.isEmpty()) {
+
+			// User supplied an expression without leading "f(...)="
+			// so we just append the user function to a proper "f()="
+			// for PostfixExpression.fromInfix()
+			StringBuilder function = new StringBuilder("f(");
+			for (String var : variables.keySet()) {
+				function.append(var).append(',');
+			}
+			expression = function.deleteCharAt(function.length() - 1).toString() + ")=" + expression;
+		}
+		// create the PostfixExpression and return it as a Calculable
+		PostfixExpression delegate = PostfixExpression.fromInfix(expression, customFunctions);
+		for (String var : variables.keySet()) {
+			if (variables.get(var) != null) {
+				delegate.setVariable(var, variables.get(var));
+			}
+			for (CustomFunction custom:customFunctions){
+				if (custom.getValue().equals(var)){
+					throw new UnparsableExpressionException("variable '" + var + "' cannot have the same name as a custom function " + custom.getValue());
+				}
+			}
+		}
+		return delegate;
+	}
+
+	/**
+	 * add a custom function instance for the evaluator to recognize
+	 * 
+	 * @param function
+	 *            the {@link CustomFunction} to add
+	 * @return the {@link ExpressionBuilder} instance
+	 */
+	public ExpressionBuilder withCustomFunction(CustomFunction function) {
+		customFunctions.add(function);
+		return this;
+	}
+
+	public ExpressionBuilder withCustomFunctions(Collection<CustomFunction> functions) {
+		customFunctions.addAll(functions);
+		return this;
+	}
+
+	/**
+	 * set the value for a variable
+	 * 
+	 * @param variableName
+	 *            the variable name e.g. "x"
+	 * @param value
+	 *            the value e.g. 2.32d
+	 * @return the {@link ExpressionBuilder} instance
+	 */
+	public ExpressionBuilder withVariable(String variableName, double value) {
+		variables.put(variableName, value);
+		return this;
+	}
+
+	/**
+	 * set the variables names used in the expression without setting their
+	 * values
+	 * 
+	 * @param variableNames
+	 *            vararg {@link String} of the variable names used in the
+	 *            expression
+	 * @return the ExpressionBuilder instance
+	 */
+	public ExpressionBuilder withVariableNames(String... variableNames) {
+		for (String variable : variableNames) {
+			variables.put(variable, null);
+		}
+		return this;
+	}
+
+	/**
+	 * set the values for variables
+	 * 
+	 * @param variableMap
+	 *            a map of variable names to variable values
+	 * @return the {@link ExpressionBuilder} instance
+	 */
+	public ExpressionBuilder withVariables(Map<String, Double> variableMap) {
+		for (Entry<String, Double> v : variableMap.entrySet()) {
+			variables.put(v.getKey(), v.getValue());
+		}
+		return this;
+	}
+}

core/src/net/sf/openrocket/util/exp4j/FunctionSeparatorToken.java

@@ -0,0 +1,17 @@
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Stack;
+
+public class FunctionSeparatorToken extends Token{
+    public FunctionSeparatorToken() {
+        super(",");
+    }
+    @Override
+    void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+        Token token;
+        while (!((token=operatorStack.peek()) instanceof ParenthesisToken) && !token.getValue().equals("(")){
+            output.append(operatorStack.pop().getValue()).append(" ");
+        }
+    }
+
+}

core/src/net/sf/openrocket/util/exp4j/FunctionToken.java

@@ -0,0 +1,127 @@
+/*
+Copyright 2011 frank asseg
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Map;
+import java.util.Stack;
+
+/**
+ * A {@link Token} for functions
+ * 
+ * @author fas@congrace.de
+ * 
+ */
+class FunctionToken extends CalculationToken {
+	/**
+	 * the functionNames that can be used in an expression
+	 * 
+	 * @author ruckus
+	 * 
+	 */
+	enum Function {
+		ABS, ACOS, ASIN, ATAN, CBRT, CEIL, COS, COSH, EXP, EXPM1, FLOOR, LOG, SIN, SINH, SQRT, TAN, TANH
+	}
+
+	private Function function;
+
+	/**
+	 * construct a new {@link FunctionToken}
+	 * 
+	 * @param value
+	 *            the name of the function
+	 * @throws UnknownFunctionException
+	 *             if an unknown function name is encountered
+	 */
+	FunctionToken(String value) throws UnknownFunctionException {
+		super(value);
+		try {
+			function = Function.valueOf(value.toUpperCase());
+		} catch (IllegalArgumentException e) {
+			throw new UnknownFunctionException(value);
+		}
+		if (function == null) {
+			throw new UnknownFunctionException(value);
+		}
+	}
+
+	/**
+	 * apply a function to a value x
+	 * 
+	 * @param x
+	 *            the value the function should be applied to
+	 * @return the result of the function
+	 */
+	double applyFunction(double x) {
+		switch (function) {
+		case ABS:
+			return Math.abs(x);
+		case ACOS:
+			return Math.acos(x);
+		case ASIN:
+			return Math.asin(x);
+		case ATAN:
+			return Math.atan(x);
+		case CBRT:
+			return Math.cbrt(x);
+		case CEIL:
+			return Math.ceil(x);
+		case COS:
+			return Math.cos(x);
+		case COSH:
+			return Math.cosh(x);
+		case EXP:
+			return Math.exp(x);
+		case EXPM1:
+			return Math.expm1(x);
+		case FLOOR:
+			return Math.floor(x);
+		case LOG:
+			return Math.log(x);
+		case SIN:
+			return Math.sin(x);
+		case SINH:
+			return Math.sinh(x);
+		case SQRT:
+			return Math.sqrt(x);
+		case TAN:
+			return Math.tan(x);
+		case TANH:
+			return Math.tanh(x);
+		default:
+			return Double.NaN; // should not happen ;)
+		}
+	}
+
+	/**
+	 * get the {@link Function}
+	 * 
+	 * @return the correspoding {@link Function}
+	 */
+	Function getFunction() {
+		return function;
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Double> stack, Map<String, Double> variableValues) {
+		stack.push(this.applyFunction(stack.pop()));
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		operatorStack.push(this);
+	}
+}

core/src/net/sf/openrocket/util/exp4j/InfixTranslator.java

@@ -0,0 +1,109 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Set;
+import java.util.Stack;
+
+/**
+ * Translate a mathematical expression in human readable infix notation to a
+ * Reverse Polish Notation (postfix) expression for easier parsing. by
+ * implementing the shunting yard algorithm by dijkstra
+ * 
+ * @author fas@congrace.de
+ */
+class InfixTranslator {
+
+	private static String substituteUnaryOperators(String expr) {
+		final StringBuilder exprBuilder = new StringBuilder(expr.length());
+		final char[] data = expr.toCharArray();
+		char lastChar = ' ';
+		for (int i = 0; i < expr.length(); i++) {
+			if (exprBuilder.length() > 0) {
+				lastChar = exprBuilder.charAt(exprBuilder.length() - 1);
+			}
+			final char c = data[i];
+			switch (c) {
+			case '+':
+				if (i > 0 && lastChar != '(' && !(OperatorToken.isOperator(lastChar))) {
+					exprBuilder.append(c);
+				}
+				break;
+			case '-':
+				if (i > 0 && lastChar != '(' && !(OperatorToken.isOperator(lastChar))) {
+					exprBuilder.append(c);
+				} else {
+					exprBuilder.append('#');
+				}
+				break;
+			default:
+				if (!Character.isWhitespace(c)) {
+					exprBuilder.append(c);
+				}
+			}
+		}
+		return exprBuilder.toString();
+	}
+
+	/**
+	 * Delegation method for simple expression without variables or custom
+	 * functions
+	 * 
+	 * @param infixExpression
+	 *            the infix expression to be translated
+	 * @return translated RNP postfix expression
+	 * @throws UnparsableExpressionException
+	 *             when the expression is invalid
+	 * @throws UnknownFunctionException
+	 *             when an unknown function has been used in the input.
+	 */
+	static String toPostfixExpression(String infixExpression) throws UnparsableExpressionException, UnknownFunctionException {
+		return toPostfixExpression(infixExpression, null, null);
+	}
+
+	/**
+	 * implement the shunting yard algorithm
+	 * 
+	 * @param infixExpression
+	 *            the human readable expression which should be translated to
+	 *            RPN
+	 * @param variableNames
+	 *            the variable names used in the expression
+	 * @param customFunctions
+	 *            the CustomFunction implementations used
+	 * @return the expression in postfix format
+	 * @throws UnparsableExpressionException
+	 *             if the expression could not be translated to RPN
+	 * @throws UnknownFunctionException
+	 *             if an unknown function was encountered
+	 */
+	static String toPostfixExpression(String infixExpression, String[] variableNames, Set<CustomFunction> customFunctions)
+			throws UnparsableExpressionException, UnknownFunctionException {
+		infixExpression = substituteUnaryOperators(infixExpression);
+		final Token[] tokens = new Tokenizer(variableNames, customFunctions).tokenize(infixExpression);
+		final StringBuilder output = new StringBuilder(tokens.length);
+		final Stack<Token> operatorStack = new Stack<Token>();
+		for (final Token token : tokens) {
+			token.mutateStackForInfixTranslation(operatorStack, output);
+		}
+		// all tokens read, put the rest of the operations on the output;
+		while (operatorStack.size() > 0) {
+			output.append(operatorStack.pop().getValue()).append(" ");
+		}
+		return output.toString().trim();
+	}
+}

core/src/net/sf/openrocket/util/exp4j/InvalidCustomFunctionException.java

@@ -0,0 +1,9 @@
+package net.sf.openrocket.util.exp4j;
+
+public class InvalidCustomFunctionException extends Exception{
+	private static final long serialVersionUID = 1L;
+
+	public InvalidCustomFunctionException(String message) {
+		super(message);
+	}
+}

core/src/net/sf/openrocket/util/exp4j/NumberToken.java

@@ -0,0 +1,66 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Map;
+import java.util.Stack;
+
+/**
+ * A {@link Token} for Numbers
+ * 
+ * @author fas@congrace.de
+ * 
+ */
+class NumberToken extends CalculationToken {
+
+	private final double doubleValue;
+
+	/**
+	 * construct a new {@link NumberToken}
+	 * 
+	 * @param value
+	 *            the value of the number as a {@link String}
+	 */
+	NumberToken(String value) {
+		super(value);
+		this.doubleValue = Double.parseDouble(value);
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (obj instanceof NumberToken) {
+			final NumberToken t = (NumberToken) obj;
+			return t.getValue().equals(this.getValue());
+		}
+		return false;
+	}
+
+	@Override
+	public int hashCode() {
+		return getValue().hashCode();
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Double> stack, Map<String, Double> variableValues) {
+		stack.push(this.doubleValue);
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		output.append(this.getValue()).append(' ');
+	}
+}

core/src/net/sf/openrocket/util/exp4j/OperatorToken.java

@@ -0,0 +1,208 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Map;
+import java.util.Stack;
+
+/**
+ * {@link Token} for Operations like +,-,*,/,% and ^
+ * 
+ * @author fas@congrace.de
+ */
+class OperatorToken extends CalculationToken {
+
+	/**
+	 * the valid {@link Operation}s for the {@link OperatorToken}
+	 * 
+	 * @author fas@congrace.de
+	 */
+	enum Operation {
+		ADDITION(1, true), SUBTRACTION(1, true), MULTIPLICATION(2, true), DIVISION(2, true), MODULO(2, true), EXPONENTIATION(3, false), UNARY_MINUS(4, false), UNARY_PLUS(
+				4, false);
+		private final int precedence;
+		private final boolean leftAssociative;
+
+		private Operation(int precedence, boolean leftAssociative) {
+			this.precedence = precedence;
+			this.leftAssociative = leftAssociative;
+		}
+	}
+
+	/**
+	 * return a corresponding {@link Operation} for a symbol
+	 * 
+	 * @param c
+	 *            the symbol of the operation
+	 * @return the corresponding {@link Operation}
+	 */
+	static Operation getOperation(char c) {
+		switch (c) {
+		case '+':
+			return Operation.ADDITION;
+		case '-':
+			return Operation.SUBTRACTION;
+		case '*':
+			return Operation.MULTIPLICATION;
+		case '/':
+			return Operation.DIVISION;
+		case '^':
+			return Operation.EXPONENTIATION;
+		case '#':
+			return Operation.UNARY_MINUS;
+		case '%':
+			return Operation.MODULO;
+		default:
+			return null;
+		}
+	}
+
+	static boolean isOperator(char c) {
+		return getOperation(c) != null;
+	}
+
+	private final Operation operation;
+
+	/**
+	 * construct a new {@link OperatorToken}
+	 * 
+	 * @param value
+	 *            the symbol (e.g.: '+')
+	 * @param operation
+	 *            the {@link Operation} of this {@link Token}
+	 */
+	OperatorToken(String value, Operation operation) {
+		super(value);
+		this.operation = operation;
+	}
+
+	/**
+	 * apply the {@link Operation}
+	 * 
+	 * @param values
+	 *            the doubles to operate on
+	 * @return the result of the {@link Operation}
+	 */
+	double applyOperation(double... values) {
+		switch (operation) {
+		case ADDITION:
+			return values[0] + values[1];
+		case SUBTRACTION:
+			return values[0] - values[1];
+		case MULTIPLICATION:
+			return values[0] * values[1];
+		case EXPONENTIATION:
+			return Math.pow(values[0], values[1]);
+		case DIVISION:
+			return values[0] / values[1];
+		case UNARY_MINUS:
+			return -values[0];
+		case UNARY_PLUS:
+			return values[0];
+		case MODULO:
+			return values[0] % values[1];
+		default:
+			return 0;
+		}
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (obj instanceof OperatorToken) {
+			final OperatorToken t = (OperatorToken) obj;
+			return t.getValue().equals(this.getValue());
+		}
+		return false;
+	}
+
+	int getOperandCount() {
+		switch (operation) {
+		case ADDITION:
+		case SUBTRACTION:
+		case MULTIPLICATION:
+		case DIVISION:
+		case EXPONENTIATION:
+		case MODULO:
+			return 2;
+		case UNARY_MINUS:
+		case UNARY_PLUS:
+			return 1;
+		default:
+			return 0;
+		}
+	}
+
+	/**
+	 * get the {@link Operation} of this {@link Token}
+	 * 
+	 * @return the {@link Operation}
+	 */
+	Operation getOperation() {
+		return operation;
+	}
+
+	int getPrecedence() {
+		return operation.precedence;
+	}
+
+	@Override
+	public int hashCode() {
+		return getValue().hashCode();
+	}
+
+	/**
+	 * check if the operation is left associative
+	 * 
+	 * @return true if left associative, otherwise false
+	 */
+	boolean isLeftAssociative() {
+		return operation.leftAssociative;
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Double> stack, Map<String, Double> variableValues) {
+		if (this.getOperandCount() == 2) {
+			final double n2 = stack.pop();
+			final double n1 = stack.pop();
+			stack.push(this.applyOperation(n1, n2));
+		} else if (this.getOperandCount() == 1) {
+			final double n1 = stack.pop();
+			stack.push(this.applyOperation(n1));
+		}
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		Token before;
+		while (!operatorStack.isEmpty() && (before = operatorStack.peek()) != null && (before instanceof OperatorToken || before instanceof FunctionToken)) {
+			if (before instanceof FunctionToken) {
+				operatorStack.pop();
+				output.append(before.getValue()).append(" ");
+			} else {
+				final OperatorToken stackOperator = (OperatorToken) before;
+				if (this.isLeftAssociative() && this.getPrecedence() <= stackOperator.getPrecedence()) {
+					output.append(operatorStack.pop().getValue()).append(" ");
+				} else if (!this.isLeftAssociative() && this.getPrecedence() < stackOperator.getPrecedence()) {
+					output.append(operatorStack.pop().getValue()).append(" ");
+				} else {
+					break;
+				}
+			}
+		}
+		operatorStack.push(this);
+	}
+}

core/src/net/sf/openrocket/util/exp4j/ParenthesisToken.java

@@ -0,0 +1,69 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Stack;
+
+/**
+ * Token for parenthesis
+ * 
+ * @author fas@congrace.de
+ */
+class ParenthesisToken extends Token {
+
+	ParenthesisToken(String value) {
+		super(value);
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (obj instanceof ParenthesisToken) {
+			final ParenthesisToken t = (ParenthesisToken) obj;
+			return t.getValue().equals(this.getValue());
+		}
+		return false;
+	}
+
+	@Override
+	public int hashCode() {
+		return getValue().hashCode();
+	}
+
+	/**
+	 * check the direction of the parenthesis
+	 * 
+	 * @return true if it's a left parenthesis (open) false if it is a right
+	 *         parenthesis (closed)
+	 */
+	boolean isOpen() {
+		return getValue().equals("(") || getValue().equals("[") || getValue().equals("{");
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		if (this.isOpen()) {
+			operatorStack.push(this);
+		} else {
+			Token next;
+			while ((next = operatorStack.peek()) instanceof OperatorToken || next instanceof FunctionToken || next instanceof CustomFunction
+					|| (next instanceof ParenthesisToken && !((ParenthesisToken) next).isOpen())) {
+				output.append(operatorStack.pop().getValue()).append(" ");
+			}
+			operatorStack.pop();
+		}
+	}
+}

core/src/net/sf/openrocket/util/exp4j/PostfixExpression.java

@@ -0,0 +1,144 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+
+/**
+ * Class for calculating values from a RPN postfix expression.<br/>
+ * The default way to create a new instance of {@link PostfixExpression} is by
+ * using the static factory method fromInfix()
+ * 
+ * @author fas@congrace.de
+ */
+public final class PostfixExpression extends AbstractExpression implements Calculable {
+	/**
+	 * Factory method for creating {@link PostfixExpression}s from human
+	 * readable infix expressions
+	 * 
+	 * @param expression
+	 *            the infix expression to be used
+	 * @return an equivalent {@link PostfixExpression}
+	 * @throws UnparsableExpressionException
+	 *             if the expression was invalid
+	 * @throws UnknownFunctionException
+	 *             if an unknown function has been used
+	 * @deprecated please use {@link ExpressionBuilder} API
+	 */
+    @Deprecated
+	public static PostfixExpression fromInfix(String expression) throws UnparsableExpressionException, UnknownFunctionException {
+		return fromInfix(expression, null);
+	}
+
+	/**
+	 * Factory method for creating {@link PostfixExpression}s from human
+	 * readable infix expressions
+	 * 
+	 * @param expression
+	 *            the infix expression to be used
+	 * @param customFunctions
+	 *            the CustomFunction implementations used
+	 * @return an equivalent {@link PostfixExpression}
+	 * @throws UnparsableExpressionException
+	 *             if the expression was invalid
+	 * @throws UnknownFunctionException
+	 *             if an unknown function has been used
+	 * @deprecated please use {@link ExpressionBuilder}
+	 */
+    @Deprecated
+	public static PostfixExpression fromInfix(String expression, Set<CustomFunction> customFunctions) throws UnparsableExpressionException,
+			UnknownFunctionException {
+		String[] variables = null;
+		int posStart, posEnd;
+		if ((posStart = expression.indexOf('=')) > 0) {
+			String functionDef = expression.substring(0, posStart);
+			expression = expression.substring(posStart + 1);
+			if ((posStart = functionDef.indexOf('(')) > 0 && (posEnd = functionDef.indexOf(')')) > 0) {
+				variables = functionDef.substring(posStart + 1, posEnd).split(",");
+			}
+		}
+		return new PostfixExpression(InfixTranslator.toPostfixExpression(expression, variables, customFunctions), variables, customFunctions);
+	}
+
+	private final Map<String, Double> variableValues = new HashMap<String, Double>();
+
+	/**
+	 * Construct a new simple {@link PostfixExpression}
+	 * 
+	 * @param expression
+	 *            the postfix expression to be calculated
+	 * @param variableNames
+	 *            the variable names in the expression
+	 * @param customFunctions
+	 *            the CustomFunction implementations used
+	 * @throws UnparsableExpressionException
+	 *             when expression is invalid
+	 * @throws UnknownFunctionException
+	 *             when an unknown function has been used
+	 */
+	private PostfixExpression(String expression, String[] variableNames, Set<CustomFunction> customFunctions) throws UnparsableExpressionException,
+			UnknownFunctionException {
+		super(expression, new Tokenizer(variableNames, customFunctions).tokenize(expression), variableNames);
+	}
+
+	/**
+	 * delegate the calculation of a simple expression without variables
+	 * 
+	 * @return the result
+	 */
+	public double calculate() {
+		return calculate(null);
+	}
+
+	/**
+	 * calculate the result of the expression and substitute the variables by
+	 * their values beforehand
+	 * 
+	 * @param values
+	 *            the variable values to be substituted
+	 * @return the result of the calculation
+	 * @throws IllegalArgumentException
+	 *             if the variables are invalid
+	 */
+	public double calculate(double... values) throws IllegalArgumentException {
+		if (getVariableNames() == null && values != null) {
+			throw new IllegalArgumentException("there are no variables to set values");
+		} else if (getVariableNames() != null && values == null && variableValues.isEmpty()) {
+			throw new IllegalAccessError("variable values have to be set");
+		} else if (values != null && values.length != getVariableNames().length) {
+			throw new IllegalArgumentException("The are an unequal number of variables and arguments");
+		}
+		int i = 0;
+		if (getVariableNames() != null && values != null) {
+			for (double val : values) {
+				variableValues.put(getVariableNames()[i++], val);
+			}
+		}
+		final Stack<Double> stack = new Stack<Double>();
+		for (final Token t : getTokens()) {
+			((CalculationToken) t).mutateStackForCalculation(stack, variableValues);
+		}
+		return stack.pop();
+	}
+
+	public void setVariable(String name, double value) {
+		variableValues.put(name, value);
+	}
+}

core/src/net/sf/openrocket/util/exp4j/Token.java

@@ -0,0 +1,50 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Stack;
+
+/**
+ * Superclass for tokenized Strings
+ * 
+ * @author fas@congrace.de
+ */
+abstract class Token {
+	private final String value;
+
+	/**
+	 * construct a new {@link Token}
+	 * 
+	 * @param value
+	 *            the value of the {@link Token}
+	 */
+	Token(String value) {
+		super();
+		this.value = value;
+	}
+
+	/**
+	 * get the value (String representation) of the token
+	 * 
+	 * @return the value
+	 */
+	String getValue() {
+		return value;
+	}
+
+	abstract void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output);
+}

core/src/net/sf/openrocket/util/exp4j/Tokenizer.java

@@ -0,0 +1,219 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import net.sf.openrocket.util.exp4j.FunctionToken.Function;
+
+/**
+ * Class for tokenizing mathematical expressions by breaking an expression up
+ * into multiple different {@link Token}s
+ * 
+ * @author fas@congrace.de
+ */
+class Tokenizer {
+	private String[] variableNames;
+	private final Set<String> functionNames = new HashSet<String>();
+	private final Set<CustomFunction> customFunctions;
+
+	{
+		functionNames.add("abs");
+		functionNames.add("acos");
+		functionNames.add("asin");
+		functionNames.add("atan");
+		functionNames.add("cbrt");
+		functionNames.add("ceil");
+		functionNames.add("cos");
+		functionNames.add("cosh");
+		functionNames.add("exp");
+		functionNames.add("expm1");
+		functionNames.add("floor");
+		functionNames.add("log");
+		functionNames.add("sin");
+		functionNames.add("sinh");
+		functionNames.add("sqrt");
+		functionNames.add("tan");
+		functionNames.add("tanh");
+	}
+
+	Tokenizer() {
+		super();
+		customFunctions = null;
+	}
+
+	/**
+	 * construct a new Tokenizer that recognizes variable names
+	 * 
+	 * @param variableNames
+	 *            the variable names in the expression
+	 * @throws IllegalArgumentException
+	 *             if a variable has the name as a function
+	 * @param customFunctions
+	 *            the CustomFunction implementations used if the variableNames
+	 *            are not valid
+	 */
+	Tokenizer(String[] variableNames, Set<CustomFunction> customFunctions) throws IllegalArgumentException {
+		super();
+		this.variableNames = variableNames;
+		if (variableNames != null) {
+			for (String varName : variableNames) {
+				if (functionNames.contains(varName.toLowerCase())) {
+					throw new IllegalArgumentException("Variable '" + varName + "' can not have the same name as a function");
+				}
+			}
+		}
+		this.customFunctions = customFunctions;
+	}
+
+	private Token getCustomFunctionToken(String name) throws UnknownFunctionException {
+		for (CustomFunction func : customFunctions) {
+			if (func.getValue().equals(name)) {
+				return func;
+			}
+		}
+		throw new UnknownFunctionException(name);
+	}
+
+	private boolean isCustomFunction(String name) {
+		if (customFunctions == null) {
+			return false;
+		}
+		for (CustomFunction func : customFunctions) {
+			if (func.getValue().equals(name)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * check if a char is part of a number
+	 * 
+	 * @param c
+	 *            the char to be checked
+	 * @return true if the char is part of a number
+	 */
+	private boolean isDigit(char c) {
+		return Character.isDigit(c) || c == '.';
+	}
+
+	private boolean isFunction(String name) {
+		for (Function fn : Function.values()) {
+			if (fn.name().equals(name.toUpperCase())) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * check if a String is a variable name
+	 * 
+	 * @param name
+	 *            the variable name which is checked to be valid the char to be
+	 *            checked
+	 * @return true if the char is a variable name (e.g. x)
+	 */
+	private boolean isVariable(String name) {
+		if (variableNames != null) {
+			for (String var : variableNames) {
+				if (name.equals(var)) {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * tokenize an infix expression by breaking it up into different
+	 * {@link Token} that can represent operations,functions,numbers,
+	 * parenthesis or variables
+	 * 
+	 * @param infix
+	 *            the infix expression to be tokenized
+	 * @return the {@link Token}s representing the expression
+	 * @throws UnparsableExpressionException
+	 *             when the expression is invalid
+	 * @throws UnknownFunctionException
+	 *             when an unknown function name has been used.
+	 */
+	Token[] tokenize(String infix) throws UnparsableExpressionException, UnknownFunctionException {
+		final List<Token> tokens = new ArrayList<Token>();
+		final char[] chars = infix.toCharArray();
+		// iterate over the chars and fork on different types of input
+		Token lastToken;
+		for (int i = 0; i < chars.length; i++) {
+			char c = chars[i];
+			if (c == ' ')
+				continue;
+			if (isDigit(c)) {
+				final StringBuilder valueBuilder = new StringBuilder(1);
+				// handle the numbers of the expression
+				valueBuilder.append(c);
+				int numberLen = 1;
+				while (chars.length > i + numberLen && isDigit(chars[i + numberLen])) {
+					valueBuilder.append(chars[i + numberLen]);
+					numberLen++;
+				}
+				i += numberLen - 1;
+				lastToken = new NumberToken(valueBuilder.toString());
+			} else if (Character.isLetter(c) || c == '_') {
+				// can be a variable or function
+				final StringBuilder nameBuilder = new StringBuilder();
+				nameBuilder.append(c);
+				int offset = 1;
+				while (chars.length > i + offset && (Character.isLetter(chars[i + offset]) || Character.isDigit(chars[i + offset]) || chars[i + offset] == '_')) {
+					nameBuilder.append(chars[i + offset++]);
+				}
+				String name = nameBuilder.toString();
+				if (this.isVariable(name)) {
+					// a variable
+					i += offset - 1;
+					lastToken = new VariableToken(name);
+				} else if (this.isFunction(name)) {
+					// might be a function
+					i += offset - 1;
+					lastToken = new FunctionToken(name);
+				} else if (this.isCustomFunction(name)) {
+					// a custom function
+					i += offset - 1;
+					lastToken = getCustomFunctionToken(name);
+				} else {
+					// an unknown symbol was encountered
+					throw new UnparsableExpressionException(c, i);
+				}
+			}else if (c == ',') {
+			    // a function separator, hopefully
+			    lastToken=new FunctionSeparatorToken();
+			} else if (OperatorToken.isOperator(c)) {
+				lastToken = new OperatorToken(String.valueOf(c), OperatorToken.getOperation(c));
+			} else if (c == '(' || c == ')' || c == '[' || c == ']' || c == '{' || c == '}') {
+				lastToken = new ParenthesisToken(String.valueOf(c));
+			} else {
+				// an unknown symbol was encountered
+				throw new UnparsableExpressionException(c, i);
+			}
+			tokens.add(lastToken);
+		}
+		return tokens.toArray(new Token[tokens.size()]);
+	}
+}

core/src/net/sf/openrocket/util/exp4j/UnknownFunctionException.java

@@ -0,0 +1,37 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+/**
+ * Exception for handling unknown Functions.
+ * 
+ * @see FunctionToken
+ * @author fas@congrace.de
+ */
+public class UnknownFunctionException extends Exception {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * construct a new {@link UnknownFunctionException}
+	 * 
+	 * @param functionName
+	 *            the function name which could not be found
+	 */
+	public UnknownFunctionException(String functionName) {
+		super("Unknown function: " + functionName);
+	}
+}

core/src/net/sf/openrocket/util/exp4j/UnparsableExpressionException.java

@@ -0,0 +1,47 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+/**
+ * Exception for invalid expressions
+ * 
+ * @author fas@congrace.de
+ */
+public class UnparsableExpressionException extends Exception {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * construct a new {@link UnparsableExpressionException}
+	 * 
+	 * @param c
+	 *            the character which could not be parsed
+	 * @param pos
+	 *            the position of the character in the expression
+	 */
+	public UnparsableExpressionException(char c, int pos) {
+		super("Unable to parse character at position " + pos + ": '" + String.valueOf(c) + "'");
+	}
+	/**
+	 * construct a new {@link UnparsableExpressionException}
+	 * 
+	 * @param msg 
+	 *            the error message
+	 */
+	public UnparsableExpressionException(String msg) {
+		super(msg);
+	}
+}

core/src/net/sf/openrocket/util/exp4j/VariableToken.java

@@ -0,0 +1,48 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package net.sf.openrocket.util.exp4j;
+
+import java.util.Map;
+import java.util.Stack;
+
+/**
+ * A {@link Token} for representing variables
+ * 
+ * @author fas
+ */
+class VariableToken extends CalculationToken {
+	/**
+	 * construct a new {@link VariableToken}
+	 * 
+	 * @param value
+	 *            the value of the token
+	 */
+	VariableToken(String value) {
+		super(value);
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Double> stack, Map<String, Double> variableValues) {
+		double value = variableValues.get(this.getValue());
+		stack.push(value);
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		output.append(this.getValue()).append(" ");
+	}
+}