How to use coeffs to a minimum power
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Connor LeClaire
on 4 Dec 2021
Commented: Star Strider
on 5 Dec 2021
Hello,
Stemming from a recent post here I wanted to ask a question about using coeffs. As the title says, is it possible to set coeffs to find all coefficients of an equation up to a power of the variable (or a minimum power if a larger power exists) for instance:
syms x
y = x + 3;
[c p] = coeffs(y,x,'all')
However in my application I need to collect all terms of x^2 from a series of equations, so for the above I would want something like:
c = (0, 1, 3)
p = (x^2, x, 1)
to make it easy. Is it possible to force coeffs to go upto a minimum power of x without altering the equation itself?
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Star Strider
on 5 Dec 2021
One approach —
syms x
eqn(1,:) = 5*x^2 + 2*x + 8;
eqn(2,:) = 42*x^3 + 3*x^2 + 3;
eqn
for k = 1:numel(eqn)
[cfs,px] = coeffs(eqn(k),'All');
xsq = find(ismember(px, x^2)); % Index Oof 'x^2' Terms
xsqcf{k} = cfs(xsq); % Coefficient Of 'x^2' Term
end
xsqcf{1}
xsqcf{2}
I have not tested this for robustness to other conditions. It works here.
.
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