How to identify repeated eigenvalues of a matrix?

You can find the number of times an eigen value is repeated as follows.

A = [1 1 0 0;0 1 1 0;0 0 1 0;0 0 0 3];
E = eig(A);
u = unique(E);
R = histc(E,u)-1;

Output is:

E =
     1
     1
     1
     3

u =
     1
     3

R =
     2
     0

NOTE: if R(i) = 0, eigen value is not repeated, but has occurred only once in vector E.