Select specific coefficient from symbolic polynomial

Given a symbolic polynomial in several variables I would like to pick the coefficient for a given monomial.

Ex: P(x,y,z)= 6*x^2*y + z*x- 5*x +7*x*y*z Let say I would like to find the coefficient of x*z in P(x,y,z) that is 1.

Or I could ask the coefficient of y in P(x,y,z) in this case I would obtain 0.

Or coefficient of x in P(x,y,z) I would obtain -5.

Is there a way to solve this?

Answer 1

[Mischa Kim]

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.

[Farid Salazar Wong]

Thanks a lot. This helped me write my own function.