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

[David Bateman]

Follow-up Comment #2, bug #29768 (project octave):

For 4) there seems to be quite a few things we might do to speed up sqrtm.
The frobnorm function seems inefficient and might be rewritten as a template
like

Template <class T>
static T
frobnorm (const Array<T>& A)
{
  T sum = T();
  T *fv = A.fortran_vec ();
  for (octave_idx_type i = 0; i < A.numel (); i++)
    sum += real(fv[i] * conj(fv[i]));
  return sqrt (sum);
}

using fortan_vec to avoid the overhead of the checking of the indexing.
Similarly the sqrtm_from_schur function might be rewritten to use fortan_vec.

The biggest gain however will come from writing the methods

ComplexMatrix schur (Matrix&, std::string&)

and

FloatComplexMatrix schur (FloatMatrix&, std::string&)

Currently in Fsqrtm. A copy of the real matrix is to a complex matrix is
made, and then in the method ComplexSCHUR::init essentially another copy of
the complex matrix is made by the copy of write to the variable schur_mat. If
the above methods are written the second of these might be avoided.

D.
 


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