It works for me in R2016a:
syms x
c = coeffs(3*x^2, 'All')
c =
[ 3, 0, 0]
The current online documentation is for R2016a. If you’re using a prior release, the online documentation might not apply. There have recently been significant changes between versions.
The sym2poly function will produce the same result if you need it for other calculations:
f = 3*x^2;
p = sym2poly(f)
p =
3 0 0
That should work in previous releases as well.
