# conditions among the variables

Suppose I am defining some variables in sagemath. How can I give conditions among the variables such that the condition is applied in the future calculations?

Thank You.

edit retag close merge delete

1

This can be done (with some effort) in many cases, depending on the type of condition. Are the conditions linear equations, polynomial equations, trigonometric equations? An example would be great.

( 2019-11-19 17:31:51 +0200 )edit

Yes, please give an example of the kind of problem you would like to solve. You can do things like assume(x > 0) or assume(x, 'complex') but whether or not that has any effect depends on what you're trying to do.

( 2019-11-20 18:25:49 +0200 )edit
1

Suppose I have variables a,b,c,d,e and I have a polynomial with these five variables.. I want to simplify the polynomial using the condition that a+b = d+e.

( 2019-11-27 04:22:48 +0200 )edit

@user789 if that's all, then just substitute e.g. $e=a+b-d$ into your polynomial.

( 2019-11-27 09:13:32 +0200 )edit

i want sage to do that for me!

( 2019-11-27 09:58:30 +0200 )edit

Sort by ยป oldest newest most voted

i want sage to do that for me!

Okay then let Sage do it for you:

sage: var('a, b, c, d, e')
(a, b, c, d, e)
sage: P = a*d + b*c + d^2 + d*e
sage: P.subs(e=(a + b - d)).expand()
b*c + 2*a*d + b*d


This is exactly what you want: It simplified the expression given that a + b = d + e.

more