How to extract powers of a symbolic polynomial?

I'm working with a symbolic polynomial

y = 0.96*z^3500 + 0.04*z^0

I can extract the coefficients easily with

coeffs(y)

but I cannot figure out a way to pull off the corresponding powers of z into a vector. I've tried doing some wonky stuff with logs, but nothing so far. Am I SOL?

Thank you!!

Answer 1

[Steven Lord]

syms z
y = 0.96*z^3500 + 0.04*z^0

y = 

[coefficients, powers] = coeffs(y)

coefficients = 

powers = 

syms y positive
exponents = simplify(subs(log(powers)./log(z), z, y))

exponents = 

[Walter Roberson]

Different formulation for finding the exponents.

syms z
y = 0.96*z^randi(9999) + 0.04*z^randi(9999)

y = 

[coefficients, powers] = coeffs(y)

coefficients = 

powers = 

exponents = mapSymType(powers, 'power', @(Z) children(Z,2));
if powers(end) == 1; exponents(end) = 0; end
exponents

exponents = 

This particular code relies on an enhancement to children() that was made a small number of releases ago. A workaround is possible for older releases.

Answer 2

[Shubham Rawat]

Hi Alina,

You may first find coefficients of all variables like this:

coef = sym2poly(y);

Then you can find all the index of all the non zero elements and -1 as indexing start from 1 in MATLAB:

polyPowers = find(coef) - 1;

Hope this Helps!

[Davy Figaro]

This is good, but because symbolic polynomial powers are presented in descending order, you need to double flip to get the polyPowers to line up to the original polynomial:

polyPowers = flip(find(flip(coef))) - 1;

Answer 3

[sil das]

(x+1)^2

[Walter Roberson]

Could you explain how that line of code solves the problem mentioend by @Alina Rossi-Conaway ?