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conditions among the variables

asked 5 years ago

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 ( 5 years ago )

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 ( 5 years ago )
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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 ( 5 years ago )

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

rburing gravatar imagerburing ( 5 years ago )

i want sage to do that for me!

user789 gravatar imageuser789 ( 5 years ago )

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answered 5 years ago

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: 5 years ago

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Last updated: Nov 27 '19