/**
* 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);
}
public boolean isConstantVar(XVariable var) {
if (!var.hasEquation()) return true;
Node eqn = var.getEquation();
if (eqn instanceof ASTConstant) return true;
/* So why would we want a=x to be treated as a constant? */
// if(eqn instanceof ASTVarNode) {
// return isConstantVar((XVariable)((ASTVarNode) eqn).getVar());
// }
return false;
}