How to extract factors of variables in an equation?

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Robert Roos
Robert Roos 2019-4-5
回答： Robert Roos 2019-4-24
I am using the symbolic toolbox to generate a set of three very big equations:
The result should be an equation of motion, so of this form:
Here q, f , τ and N are vectors of three elements and M and C are 3x3.
If I have a variable with the vector 'f', is there a way of find the matrices M and C?
I found the `collect` function, which orders an equation into polynomials with respect to a variable and this can be easily used to manually find those matrices, however, the rest of the equation remains, so it cannot be automated.
Example, say the function is I want to extract the factors 10, 7 and -1 for the three states respectively as seperate variables.

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Robert Roos
Robert Roos 2019-4-24
I ended up accomplishing this using coeffs: (Thanks to madhan ravi)
for i = 1:N
for j = 1:N
% M matrix
cM = coeffs(eom(i), ddq(j), 'All');
if length(cM) > 2
error('Polynomial in mass-matrix count not equal to 2, equation is not linear to mass');
end
if length(cM) == 2
M(i,j) = cM(1);
else
M(i,j) = 0;
end
end
end
I look at the coefficients for each equation with respect to each state and put the result in the matrix.

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