public int extent(ExpressionProgram prog, int myIndex) {
// The ExpressionCommand occurs in the program prog at the index indicated by myIndex.
// Return the total number of indices in prog occupied by this command and the commands
// that generate data used by this command. In this case, that means the commands that
// compute the upper and lower limits of the summatio, plus this Cmd object.
int upper = prog.extent(myIndex - 1); // Extent of upper limit expression in prog.
int lower = prog.extent(myIndex - 1 - upper); // Extent of lower limit expression in prog.
return upper + lower + 1; // Upper + lower limits + this object.
}
public void appendOutputString(ExpressionProgram prog, int myIndex, StringBuffer buffer) {
// The ExpressionCommand occurs in the program prog at the index indicated by myIndex.
// Add a print string representation of the sub-expression represented by this command
// (including any previous commands in the program that generate data used by this
// command).
int upper = prog.extent(myIndex - 1);
buffer.append("sum(");
buffer.append(sumVar.getName());
buffer.append(", ");
prog.appendOutputString(myIndex - 1 - upper, buffer);
buffer.append(", ");
prog.appendOutputString(myIndex - 1, buffer);
buffer.append(", ");
buffer.append(sumExpr.toString());
buffer.append(")");
}
/**
* When the name of this ParserExtension is encountered by a parser with which the extension is
* registered, the parser calls this routine to parse the summation subexpression. The
* subexpression has the form (<variable>,<lower-limit>,<upper-limit>,<expression>). This method
* is not meant to be called directly
*/
public void doParse(Parser parser, ParserContext context) {
int tok = context.next();
String open = context.tokenString;
if (tok == ParserContext.OPCHARS
&& (open.equals("(")
|| (open.equals("[") && (context.options & Parser.BRACKETS) != 0)
|| (open.equals("{") && (context.options & Parser.BRACES) != 0))) {
String close = open.equals("(") ? ")" : (open.equals("[") ? "]" : "}");
tok = context.next(); // Must be an identifier.
if (tok != ParserContext.IDENTIFIER)
throw new ParseError(
"Expected the summation variable as the first argument of " + name + ".", context);
String varName = context.tokenString;
tok = context.next();
if (tok != ParserContext.OPCHARS || !context.tokenString.equals(","))
throw new ParseError(
"Exprected a comma after the index variable, " + varName + ".", context);
parser.parseExpression(context);
tok = context.next();
if (tok != ParserContext.OPCHARS || !context.tokenString.equals(","))
throw new ParseError(
"Exprected a comma after the lower limit expression for " + name + ".", context);
parser.parseExpression(context);
tok = context.next();
if (tok != ParserContext.OPCHARS || !context.tokenString.equals(","))
throw new ParseError(
"Exprected a comma after the upper limit expression for " + name + ".", context);
Variable v = new Variable(varName);
context.mark(); // Temporoarily add the summation variable to the symbol table.
context.add(v);
ExpressionProgram saveProg = context.prog;
context.prog = new ExpressionProgram(); // Compile the expression into a new program.
parser.parseExpression(context);
tok = context.next();
if (tok != ParserContext.OPCHARS || !context.tokenString.equals(close))
throw new ParseError(
"Expected a \"" + close + "\" at the end of the paramter list for " + name + ".",
context);
context.revert(); // Restore the state of the ParserContext.
saveProg.addCommandObject(new Cmd(v, context.prog));
context.prog = saveProg;
} else throw new ParseError("Parentheses required around parameters of summation.", context);
} // end doParse()
public void compileDerivative(
ExpressionProgram prog, int myIndex, ExpressionProgram deriv, Variable wrt) {
// The ExpressionCommand occurs in the program prog at the index indicated by myIndex.
// Add commands to deriv that will evaluate the derivative of this command with respect to
// the variable wrt. Note that the "Cmd" object is preceded in the program by commands that
// compute the lower and upper limits of the summation.
if (!sumExpr.dependsOn(wrt)) deriv.addConstant(0);
else {
int upper = prog.extent(myIndex - 1); // Size of expression giving the upper limit.
prog.copyExpression(myIndex - 1 - upper, deriv); // Copy lower limit exression to deriv.
prog.copyExpression(myIndex - 1, deriv); // Copy upper limit expression to deriv.
deriv.addCommandObject(new Cmd(sumVar, (ExpressionProgram) sumExpr.derivative(wrt)));
}
}
public void apply(StackOfDouble stack, Cases cases) {
// This routine is called when an ExpressionCommand object is encountered during
// the evaluation of an ExpressionProgram. The stack may contain results of
// previous commands in the program. In this case, the command is a summation
// and the stack contains the upper and lower limits summation limits.
double upper = Math.round(stack.pop()) + 0.1; // Get summation limits.
double lower = Math.round(stack.pop());
if (Double.isNaN(upper) && Double.isNaN(lower) || upper - lower > 1000000)
stack.push(Double.NaN);
double sum = 0;
for (double x = lower; x <= upper; x++) { // Compute the sum.
sumVar.setVal(x);
sum += sumExpr.getVal();
}
stack.push(sum); // Leave the sum on the stack.
}
public boolean dependsOn(Variable x) {
// Return true if this command depends on the value of x, false otherwise.
// That is, when apply() is called, can the result depend on the value of x?
return sumExpr.dependsOn(x);
}
