Save each iteration of a for loop to table

I'm trying to calculate the roots of a cubic polynomial for several different values. This is the original polynomial, in case that helps:

I'm not confused about getting the coefficients, that isn't the issue. I'm trying to get the roots of alpha for several values of alpha_0, and I want to save them all in one table or matrix so that I can use the data to generate multiple plots.

for alpha_0 = [-1 -0.5 -0.1 0 0.1 0.5 1]

for alpha = zeros()

p = [1 2*alpha_0, alpha_0^2, -1/2];

r = roots(p);

alpha = [; r];

Roots = array2table(alpha)

end

end

This is the code I have currently, but it rewrites my output each time. Could anyone advise on how I can save all roots of alpha for all values of alpha_0 in the one matrix and/or table? Thanks so much!

Answer 1

[Stephen23]

With MATLAB it is invariably easier to loop over indices, rather than looping over data values directly.

V =  [-1,-0.5,-0.1,0,0.1,0.5,1];
N = numel(V);
R = nan(3,N);
for k = 1:N % loop over indices
    p = [1,2*V(k),V(k)^2,-1/2];
    R(:,k) = roots(p);
end
display(R)

R = 
   1.5652 + 0.0000i   1.1573 + 0.0000i   0.8617 + 0.0000i  -0.3969 + 0.6874i  -0.4642 + 0.6862i  -0.7500 + 0.6614i  -1.1486 + 0.6028i
   0.2174 + 0.5217i  -0.0786 + 0.6526i  -0.3309 + 0.6861i  -0.3969 - 0.6874i  -0.4642 - 0.6862i  -0.7500 - 0.6614i  -1.1486 - 0.6028i
   0.2174 - 0.5217i  -0.0786 - 0.6526i  -0.3309 - 0.6861i   0.7937 + 0.0000i   0.7285 + 0.0000i   0.5000 + 0.0000i   0.2972 + 0.0000i

[Emma Stanton]

Thank you very much!

I'm now trying to separate them into real and imaginary parts. I've tried adding real = real(R) and imag = imag(R) at the end of the code there, but am getting error messages. Do you have any suggestions for this? Your help is much appreciated!

[Stephen23]

"I've tried adding real = real(R) and imag = imag(R) at the end of the code there, but am getting error messages"

Do not use variable names that are the same as the function names.

V =  [-1,-0.5,-0.1,0,0.1,0.5,1];
N = numel(V);
R = nan(3,N);
for k = 1:N % loop over indices
    p = [1,2*V(k),V(k)^2,-1/2];
    R(:,k) = roots(p);
end
R_real = real(R)

R_real = 3×7

1.5652 1.1573 0.8617 -0.3969 -0.4642 -0.7500 -1.1486 0.2174 -0.0786 -0.3309 -0.3969 -0.4642 -0.7500 -1.1486 0.2174 -0.0786 -0.3309 0.7937 0.7285 0.5000 0.2972

R_imag = imag(R)

R_imag = 3×7

0 0 0 0.6874 0.6862 0.6614 0.6028 0.5217 0.6526 0.6861 -0.6874 -0.6862 -0.6614 -0.6028 -0.5217 -0.6526 -0.6861 0 0 0 0