# Difference Between Constants and Variables

Hello all. I'm working with variational calculus in sage and working with complicate expression F of a lot of variables declared with var. I used var to declare both variables and constants. My problem is that I have to know the exact number of variables which some generic expression depends. By this reason the member function variables of an expression does not work, i.e., it returs both variables and constants because them was declared with var function. I'm wondering if there is some type of variable in sage that can act as a variable to construct an expression and don't be returned by the variables member function.

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Could you please give an example of your expression, and tell us what you consider as variable and what you consider as constant in your example ?

( 2013-10-08 13:17:18 +0200 )edit

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I am not sur it answers the question :

def dependance(f):
dep = []
for var in variables:
if diff(f, var) != 0:
dep.append(var)
return dep

variables = var('x y z')
constants = var('A B C')

f = A*x + z^2/B + C
print dependance(f)

It returns [x, z].

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Hello thaks for your answer, but that is not that I'm looking for, because in your method you have to set a priori the set list variables that you are using.

( 2013-10-09 12:40:39 +0200 )edit