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conditions among the variables

asked 2019-11-19 13:55:04 +0200

user789 gravatar image

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.

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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.

rburing gravatar imagerburing ( 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.

Iguananaut gravatar imageIguananaut ( 2019-11-20 18:25:49 +0200 )edit

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.

user789 gravatar imageuser789 ( 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.

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

i want sage to do that for me!

user789 gravatar imageuser789 ( 2019-11-27 09:58:30 +0200 )edit

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answered 2019-11-27 12:43:59 +0200

Iguananaut gravatar image

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.

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Asked: 2019-11-19 13:55:04 +0200

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Last updated: Nov 27 '19