Error when working with a derivative
- To: mathgroup at smc.vnet.net
- Subject: [mg104947] Error when working with a derivative
- From: Vicent <vginer at gmail.com>
- Date: Sat, 14 Nov 2009 01:57:05 -0500 (EST)
Hello.
This is my first message to the list.
I work with Mathematica 7.0.0 on Windows.
I work with a multiple-variable function, say "MuVaF", and I want to
define a function which is the partial derivative with respect to one
of the variables. I tried with this:
MuVaF[ex_, ey_] := ex^2 + ey^2 + ex*ey + ex + ey
Then, if I try to derivate it with respect to "ex":
D[MuVaF[ex, ey], ex]
I get this:
1 + 2 ex + ey
Which sound OK to me. But if I try this:
DerivMuVaF[ex_, ey_] := D[MuVaF[ex, ey], ex]
And then this (trying to evaluate the function for a given point):
DerivMuVaF[1, 2]
I get an error message:
General::ivar: 1 is not a valid variable. >>
I think that's because Mathematica is understanding I am trying to
perform the derivative on "1"; it is expecting to get a variable and I
am giving a number instead. So, what's the right way to tell
Mathematica I want to work with the derivative function of a
previously defined function??
I guess the answer should be easy, but I haven't been able to find it
out by my own. :-(
Thank you in advance for your answers!
--
Vicent Giner-Bosch
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