[Octave-bug-tracker] [bug #29768] logm fix

[Jaroslav Hajek]

Follow-up Comment #7, bug #29768 (project octave):

I removed the old unconditional error checks because Matlab doesn't seem to
do them either:
>> sqrtm([1 -1 -1; 0 1 -1; 0 1 -1]) 

ans =

   1.0e+08 *

    0.0000    1.0183   -1.0183
         0    0.5092   -0.5092
         0    0.5092   -0.5092


I believe the residual argument is intended to verify the result:

octave:1> [x,err] = sqrtm([1 -1 -1; 0 1 -1; 0 1 -1])
warning: sqrtm: matrix is singular, may not have a square root
x =

  1.0000e+00 + 0.0000e+00i  -3.0000e+00 - 1.3422e+08i  1.0000e+00 +
1.3422e+08i
  0.0000e+00 + 0.0000e+00i  0.0000e+00 - 6.7109e+07i  0.0000e+00 +
6.7109e+07i
  0.0000e+00 + 0.0000e+00i  0.0000e+00 - 6.7109e+07i  0.0000e+00 +
6.7109e+07i

err =  1.9640

isntead of computing the exact residual (which can be costly), Matlab also
allows estimating it using a special power method technique. Octave currently
can't.



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