MATLAB: Diag problem while substracting

diagsubstract;wrong answer

my rho total is a square matrix, and when I do that:
 diag(rho_total-1)
it gives me
 1.0e-15 *
   0.444089209850063
   0.444089209850063
  -0.111022302462516
  -0.111022302462516
  -0.222044604925031
   0.666133814775094
why is that e-15 there?

Best Answer

It's just a display format thing. It means each number shown is actually multiplied by 1.0e-15
E.g.,
>> [1 2 3]
ans =
     1     2     3
>> [1e-16 2e-16 3e-16]
ans =
  1.0e-015 *
    0.1000    0.2000    0.3000
So the diagonal numbers of rho_total you show in your post were actually pretty close to 1, since the difference between them and 1 is close to eps(1).
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