# [Maxima] assigning a value to x in diff(f(x),x)

nijso beishuizen nijso at hotmail.com
Sun Apr 8 04:54:56 CDT 2012

```Thanks! This looks promising.
is at(F(x,y),[x=0,y=0]) the same as F(0,0) when no derivatives are involved?

I still need to know which variables, if any, are involved in differential operators.
I now declare dependencies to deal with this (using atvalue, assuming all dependencies are involved in differentiation), but if somebody knows a more elegant method of finding the free dependent variables in an expression, please let me know.

Date: Fri, 6 Apr 2012 15:13:02 -0700
From: fateman at eecs.berkeley.edu
To: nijso at hotmail.com
Subject: Re: [Maxima] assigning a value to x in diff(f(x),x)

try looking at   "at"

On 4/6/2012 1:59 PM, nijso beishuizen wrote:

Dear all,

I have written a function separable(expr,x,y) that returns
[f(x),g(y)] if expr is separable, and false otherwise.

However, I have a problem with the exotic case where expr
contains the derivative of an unknown function f(x), i.e. when
expr:diff(f(x),x)*y

The problem is that the algorithm works by assigning a value to
x.

Is there a way to make 'something like this' work:

depends(f,x);

define(F(x),diff(f,x));

F(0);

which should then result in the equivalent of  f '(0).

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