different results in R2012x and R2013x of function eig for matrices of class sym

whos Name Size Bytes Class Attributes

a         1x1               112  sym              
mat       5x5               112  sym

a =

a

mat =

[   1, a^2, a^2, a^2, a]
[ a^2,   1, a^2, a^2, a]
[ a^2, a^2,   1, a^2, a]
[ a^2, a^2, a^2,   1, a]
[   a,   a,   a,   a, 1]

The result of

simplify(prod(eig(mat)))

is up to MATLAB_R2012b

(a^2 - 1)^4

which is the expected result.

Since MATLAB_R2013a the outcome is

(a^2 - 1)^2

How can it be fixed in R2013x?

[Roger Stafford]

Yes, (1-a^2)^4 is the correct result. Even my ancient twenty-year-old version of Symbolic Toolbox gets it right. If R2013a gets (1-a^2)^2, that is surely a bug and should be reported to Mathworks.

Answer 1

[Sean de Wolski]

I can reproduce this. Please contact support.