check if symbolic expression contains a variable

Question

check if symbolic expression contains a given variable

Is there a function or method that tests a symbolic expression <type 'sage.symbolic.expression.expression'=""> to see if it contains a particular variable?

For example to test y(x) == -3/(x^3 + 3c + 3x) to see if it contains the variable c.

(I'm trying to write a a program to automatically plot the return value of the differential equation function desolve(), and it would help to be able to detect if the return expression contains the 'arbitrary constant' c.)

Answer 1

4	You can also use the `has()` method for an expression: `sage: var('x,c') sage: y(x)=-3/(x^3 + 3c + 3x) sage: y.has(c) True` example on aleph.sagemath.org link posted May 04 '12 Mike Hansen 3675 ● 19 ● 43 ● 81

Answer 2

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Try the .variables() method for an expression:

var('x,c')
y(x)=-3/(x^3 + 3*c + 3*x)
print y.variables()
c in y.variables()

http://aleph.sagemath.org/?q=aefb061f-d758-499c-b4b3-b209efbf6240

link

posted May 04 '12

Jason Grout
3185 ● 7 ● 27 ● 71

updated May 04 '12

Thanks, Mike and Jason. Both methods work very nicely in my program.

leonardo (May 05 '12)

check if symbolic expression contains a variable

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