private static Node DAtan(FunctionNode f, IReadOnlyList <Node> dargs) => dargs.Check(1)[0] / (Node.One + Node.Power(f.Arguments[0], Node.Two));
/// <summary>
/// Derives the specified node to the variables.
/// </summary>
/// <param name="node">The nodes.</param>
/// <returns>The derived nodes, or <c>null</c> if all derivatives are zero.</returns>
public virtual Dictionary <VariableNode, Node> Derive(Node node)
{
if (Variables == null)
{
return(null);
}
// We can skip anything that is constant!
if ((node.Properties & NodeProperties.Constant) != 0)
{
return(null);
}
Dictionary <VariableNode, Node> a = null, b = null;
switch (node)
{
case UnaryOperatorNode un:
if (un.NodeType == NodeTypes.Not)
{
return(null);
}
a = Derive(un.Argument);
switch (un.NodeType)
{
case NodeTypes.Plus: return(Apply(a, n => Node.Plus(n)));
case NodeTypes.Minus: return(Apply(a, n => Node.Minus(n)));
}
break;
case BinaryOperatorNode bn:
switch (bn.NodeType)
{
case NodeTypes.And:
case NodeTypes.Or:
case NodeTypes.Xor:
case NodeTypes.GreaterThan:
case NodeTypes.GreaterThanOrEqual:
case NodeTypes.LessThan:
case NodeTypes.LessThanOrEqual:
case NodeTypes.Equals:
case NodeTypes.NotEquals:
return(null);
}
a = Derive(bn.Left);
b = Derive(bn.Right);
switch (bn.NodeType)
{
case NodeTypes.Add: return(Combine(a, b, n1 => n1, n2 => n2));
case NodeTypes.Subtract: return(Combine(a, b, n1 => n1, n2 => Node.Minus(n2), (n1, n2) => Node.Subtract(n1, n2)));
case NodeTypes.Multiply: return(Combine(a, b, n1 => n1 * bn.Right, n2 => bn.Left * n2));
case NodeTypes.Divide:
return(Combine(a, b,
n1 => n1 / bn.Right,
n2 => - (n2 / Node.Power(bn.Right, Node.Two)),
(n1, n2) => (n1 * bn.Right - bn.Left * n2) / Node.Power(bn.Right, Node.Two)));
case NodeTypes.Pow:
return(Combine(a, b,
n1 => n1 * bn.Right * Node.Power(bn.Left, bn.Right - Node.One),
n2 => n2 * Node.Function("log", bn.Left) * bn));
case NodeTypes.Modulo:
return(Combine(a, b,
n1 => n1,
n2 => n2 * -bn,
(n1, n2) => n1 - n2 * bn));
}
break;
case TernaryOperatorNode tn:
a = Derive(tn.IfTrue);
b = Derive(tn.IfFalse);
return(Combine(a, b,
n1 => Node.Conditional(tn.Condition, n1, Node.Zero),
n2 => Node.Conditional(tn.Condition, Node.Zero, n2),
(n1, n2) => Node.Conditional(tn.Condition, n1, n2)));
case FunctionNode fn:
if (fn.Arguments.Count == 0)
{
return(null);
}
// Build the derived arguments
var lst = new Dictionary <VariableNode, Node[]>(Variables.Comparer);
for (var i = 0; i < fn.Arguments.Count; i++)
{
var darg = Derive(fn.Arguments[i]);
if (darg != null)
{
foreach (var pair in darg)
{
if (!lst.TryGetValue(pair.Key, out var dargs))
{
dargs = new Node[fn.Arguments.Count];
lst.Add(pair.Key, dargs);
}
dargs[i] = pair.Value;
}
}
}
// If there are no derivative, let's just stop here
if (lst.Count == 0)
{
return(null);
}
// Give a chance to our function rules
if (FunctionRules == null || !FunctionRules.TryGetValue(fn.Name, out var rule))
{
rule = (fn, darg) => ChainRule(fn, darg, "d{0}({1})");
}
a = new Dictionary <VariableNode, Node>(Variables.Comparer);
foreach (var pair in lst)
{
var df = rule(fn, pair.Value);
if (df != null)
{
a.Add(pair.Key, df);
}
}
// If all derivatives are zero, return null
return(a.Count > 0 ? a : null);
case VariableNode vn:
if (Variables.Contains(vn))
{
a = new Dictionary <VariableNode, Node>(Variables.Comparer)
{
{ vn, Node.One }
};
return(a);
}
return(null);
case PropertyNode _:
case ConstantNode _:
return(null);
}
throw new Exception("Could not derive expression node {0}".FormatString(node));
}
private static Node DAsin(FunctionNode f, IReadOnlyList <Node> dargs) => dargs.Check(1)[0] / Node.Function("sqrt", Node.One - Node.Power(f.Arguments[0], Node.Two));
