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

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?

Answer 1

[Paul]

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