/// <summary>
/// Calculates the gradient (first derivative) of a node with respect to a parameter node passed (pointer node).
/// This method calls FNodeCompacter.CompactNode if the class level static variable 'Compact' is true (by default it is set to true).
/// The gradient calculation leaves a lot of un-needed expressions that could be cancled out.
/// </summary>
/// <param name="Node">The node to calculate the gradient over</param>
/// <param name="X">The parameter we are differentiating with respect to</param>
/// <returns>A node representing a gradient</returns>
internal static FNode Gradient(FNode Node, FNodePointer X)
{
// The node is a pointer node //
if (Node.Affinity == FNodeAffinity.PointerNode)
{
if ((Node as FNodePointer).PointerName == X.PointerName)
return new FNodeValue(Node.ParentNode, Cell.OneValue(X.ReturnAffinity()));
else
return new FNodeValue(Node.ParentNode, Cell.ZeroValue(X.ReturnAffinity()));
}
// The node is not a function node //
if (Node.Affinity != FNodeAffinity.ResultNode)
return new FNodeValue(Node.ParentNode, Cell.ZeroValue(Node.ReturnAffinity()));
// Check if the node, which we now know is a function, has X as a decendant //
if (!FNodeAnalysis.IsDecendent(X, Node))
return new FNodeValue(Node.ParentNode, Cell.ZeroValue(X.ReturnAffinity()));
// Otherwise we have to do work :( //
// Get the name signiture //
string name_sig = (Node as FNodeResult).InnerFunction.NameSig;
// Go through each differentiable function //
FNode t = null;
switch (name_sig)
{
case FunctionNames.UNI_PLUS:
t = GradientOfUniPlus(Node, X);
break;
case FunctionNames.UNI_MINUS:
t = GradientOfUniMinus(Node, X);
break;
case FunctionNames.OP_ADD:
t = GradientOfAdd(Node, X);
break;
case FunctionNames.OP_SUB:
t = GradientOfSubtract(Node, X);
break;
case FunctionNames.OP_MUL:
t = GradientOfMultiply(Node, X);
break;
case FunctionNames.OP_DIV:
t = GradientOfDivide(Node, X);
break;
case FunctionNames.FUNC_LOG:
t = GradientOfLog(Node, X);
break;
case FunctionNames.FUNC_EXP:
t = GradientOfExp(Node, X);
break;
case FunctionNames.FUNC_POWER:
t = GradientOfPowerLower(Node, X);
break;
case FunctionNames.FUNC_SIN:
t = GradientOfSin(Node, X);
break;
case FunctionNames.FUNC_COS:
t = GradientOfCos(Node, X);
break;
case FunctionNames.FUNC_TAN:
t = GradientOfTan(Node, X);
break;
case FunctionNames.FUNC_SINH:
t = GradientOfSinh(Node, X);
break;
case FunctionNames.FUNC_COSH:
t = GradientOfCosh(Node, X);
break;
case FunctionNames.FUNC_TANH:
t = GradientOfTanh(Node, X);
break;
case FunctionNames.FUNC_LOGIT:
t = GradientOfLogit(Node, X);
break;
case FunctionNames.FUNC_NDIST:
t = GradientOfNDIST(Node, X);
break;
default:
throw new Exception(string.Format("Function is not differentiable : {0}", name_sig));
}
if (Compact)
t = FNodeCompacter.CompactNode(t);
return t;
}
