MATLAB: Extract num and den in symbolic expression.

Question

The 'tf' function in Control Systems needs numerator and denometer in a vector of decreasing powers of s.

For example a numerator of a*s^2 + b*s + c needs to be num= [a b c];. I have been cutting and pasting the necessary coefficients

but to do this I have to pause my program. Is there a way to extract the appropriate vector(s) programatically?

Thanks,

Bruce Taylor

Answer 1

Use the sym2poly funciton:

syms a b c s 
num = 1*s^2 + 2*s + 3;
n = sym2poly(num)
n = 
     1     2     3