/**
* Differentiates a variable. May want to alter behaviour when using multi equation as diff(f,x)
* might not be zero.
*
* @return 1 if the variable has the same name as data, 0 if the variable has a different name.
*/
public Object visit(ASTVarNode node, Object data) throws ParseException {
String varName = (String) data;
XVariable var = (XVariable) node.getVar();
PartialDerivative deriv = null;
if (var instanceof DVariable) {
DVariable difvar = (DVariable) var;
if (varName.equals(var.getName())) return nf.buildConstantNode(tu.getONE());
else if (isConstantVar(var)) return nf.buildConstantNode(tu.getZERO());
deriv = difvar.findDerivative(varName, localDJep);
} else if (var instanceof PartialDerivative) {
if (isConstantVar(var)) return nf.buildConstantNode(tu.getZERO());
PartialDerivative pvar = (PartialDerivative) var;
DVariable dvar = pvar.getRoot();
deriv = dvar.findDerivative(pvar, varName, localDJep);
} else throw new ParseException("Encountered non differentiable variable");
Node eqn = deriv.getEquation();
if (eqn instanceof ASTVarNode) return nf.buildVariableNode(((ASTVarNode) eqn).getVar());
if (eqn instanceof ASTConstant) return nf.buildConstantNode(((ASTConstant) eqn).getValue());
return nf.buildVariableNode(deriv);
}
/** multi dimensional differentiable variables */
public Object visit(ASTVarNode node, Object data) throws ParseException {
MatrixVariableI var = (MatrixVariableI) node.getVar();
if (var.hasValidValue()) return var.getMValue();
if (!var.hasEquation())
throw new ParseException(
"Tried to evaluate a variable with an invalid value but no equation");
MatrixValueI res = (MatrixValueI) var.getEquation().jjtAccept(this, data);
var.setMValue(res);
return res;
}
/**
* creates a new ASTVarNode with the same name as argument.
*
* @throws ParseException
*/
public ASTVarNode buildVariableNode(ASTVarNode node) throws ParseException {
return buildVariableNode(node.getVar());
}