Partial derivative function definitions

• To: mathgroup at smc.vnet.net
• Subject: [mg127531] Partial derivative function definitions
• From: "Mat' G\." <ellocomateo at free.fr>
• Date: Thu, 2 Aug 2012 04:50:42 -0400 (EDT)
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• Delivered-to: l-mathgroup@wolfram.com
• Delivered-to: mathgroup-newout@smc.vnet.net
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```Hello,
Can someone please explain me why the following partial derivative
function definitions do not work? I get errors like:
General::ivar: -6.28229 is not a valid variable. >>
General::ivar: -5.38469 is not a valid variable. >>
General::ivar: -4.48709 is not a valid variable. >>
General::stop: Further output of General::ivar will be suppressed during
this calculation. >>

Thanks for helping!
Mat

XFunction[x_, y_] := Sin[x] Sin[y];
YFunction[x_, y_] := Cos[x] Cos[y];
dXFunctiondx[x_, y_] := D[XFunction[x, y], x];
dXFunctiondy[x_, y_] := D[XFunction[x, y], y];
dYFunctiondx[x_, y_] := D[YFunction[x, y], x];
dYFunctiondy[x_, y_] := D[YFunction[x, y], y];

Grid[{
{
DensityPlot[
XFunction[x, y], {x, -2 \[Pi], 2 \[Pi]}, {y, -2 \[Pi], 2 \[Pi]}]
, DensityPlot[
YFunction[x, y], {x, -2 \[Pi], 2 \[Pi]}, {y, -2 \[Pi], 2 \[Pi]}]
}
, {
DensityPlot[
dXFunctiondx[x, y], {x, -2 \[Pi], 2 \[Pi]}, {y, -2 \[Pi], 2 \[Pi]}]
, DensityPlot[
dYFunctiondx[x, y], {x, -2 \[Pi], 2 \[Pi]}, {y, -2 \[Pi], 2 \[Pi]}]
}
, {
DensityPlot[
dXFunctiondy[x, y], {x, -2 \[Pi], 2 \[Pi]}, {y, -2 \[Pi], 2 \[Pi]}]
, DensityPlot[
dYFunctiondy[x, y], {x, -2 \[Pi], 2 \[Pi]}, {y, -2 \[Pi], 2 \[Pi]}]
}
}]

```

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