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## matrix_type problems

**From**: |
Vic Norton |

**Subject**: |
matrix_type problems |

**Date**: |
Sat, 2 Dec 2006 14:02:18 -0500 |

The idea of a matrix_type function makes a lot of sense to me, but what we have
now doesn't seem to work in Octave 2.9.9.
For example:
octave> A = eye(5)
A =
1 0 0 0 0
0 1 0 0 0
0 0 1 0 0
0 0 0 1 0
0 0 0 0 1
octave> matrix_type(A)
ans = Upper
octave> A(2,1) = 1
A =
1 0 0 0 0
1 1 0 0 0
0 0 1 0 0
0 0 0 1 0
0 0 0 0 1
octave> matrix_type(A)
ans = Upper
It would be great if octave could take advantage of upper triangular structure,
but the above exercise doesn't give me much confidence.
I would also like to see a simple test of whether a matrix is upper triangular.
Obviously
octave> strcmp(matrix_type(A), "Upper")
ans = 1
doesn't work, because matrix_type (with one argument) doesn't work.
Regards,
Vic

**matrix_type problems**,
*Vic Norton* **<=**