Farid, you can back out the subexpressions and the corresponding coefficients of the polynomial using coeffs
syms x y z P(x,y,z)
P(x,y,z) = 6*x^2*y + z*x- 5*x +7*x*y*z;
[c,t] = coeffs(P)
c(x, y, z) =
[ 6, 7, 1, -5]
t(x, y, z) =
[ x^2*y, x*y*z, x*z, x]
With this approach and a bit of logic you can write a function that returns the coefficient as stated in your question.
