Attempt to have a 3D mesh plot of max value of real part of eigenvalues of a matrix. Shows error saying that 'Error showing Horzcat. CAT arguments dimensions are not consistent' even though my matrix is square.

Here is my code:

[B,k]=meshgrid(0:0.01:10);

BKm= [0,  1,  0,  0,  0,  0;
(-0.0517428 *k-0.444277),  (-0.260491),  (0.112669 *k+0.135935),  (0.711674),  (-0.12895 *k-1.63146),  (-0.711674);
0,  0,  0,  1,  0,  0;
(0.141364 *k+1.21379),  (0.711674),  (0.0374225-0.294178 *k),  (-1.94433),  (0.325021 *k+3.63963),  (1.94433);
0,  0,  0,  0,  0,  1;
(-0.141364 *k-1.21379),  (-0.711674),  (0.270554 *k-0.745489),  (1.94433),  (-0.301397 *k-2.93156),  (-1.94433)
];

EV=eig(BKm);
Eigmax=max(real(EV));
surf(k,B,BKm)

And the error:

Error using horzcat
CAT arguments dimensions are not consistent.

I am attempting to plot the maximum of real parts of all eigenvalues available for this matrix in a 3D contour sort of plot. Even though my matrix seems square to me, I am getting this error. Please help. Thanks in advance.

Answer 1

[Kye Taylor]

When you create BKm, you use the output k from meshgrid. The output k is a 1001 square matrix that you are effectively trying to use as a scalar in the definition of BKm.

If k were a scalar, BKm would be a 6-by-6 square matrix so the surf command won't work unless BKm is the same size as k, which must also be the same size as B in order for surf() to work.

Answer 2

[Walter Roberson]

k is 1001 by 1001. a*k+b with a and b scalar would then be 1001 x 1001. You then try to horzcat a 1 x 1 scalar -0.260491 with that (second line of matrix). Dimension problems.

What are you trying to do, create a 4D matrix, 6 x 6 x 1001 x 1001 ? If you do, you will not be able to eig() that matrix.