how to make a sum of squares symbollically known to MATLAB for use in simplification

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I have a complex symbolic expression like
f = (a) * (b) * (c) * (1- x^2 - y^2 - z^2) * (d)
I would likt to try to tell matlab that (1- x^2 - y^2 - z^2) = 0
so that when I execute simpify(f) or eval(f) I would get f=0
I try
assume((1- x^2 - y^2 - z^2) == 0).
That does not work
I try
z = sqrt(1 - x^2 - y^2)
That does not work
How can I do this?

Answers (1)

Paul
Paul on 27 Oct 2022
Hi Michael,
simplify works for this case:
syms a b c d x y z
f = (a) * (b) * (c) * (1- x^2 - y^2 - z^2) * (d)
f = 
assume(1 - x^2 - y^2 - z^2 == 0)
simplify(f)
ans = 
0

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