GNU Octave Manual Version 3by John W. Eaton, David Bateman, Søren Hauberg Paperback (6"x9"), 568 pages ISBN 095461206X RRP £24.95 ($39.95) |

### 20.1.4 Sparse Matrix Types

When solving linear equations involving sparse matrices Octave
determines the appropriate algorithm from the properties of the
matrix, as discussed in section 20.2 Linear Algebra on Sparse Matrices. Octave probes the
matrix type when the div (`/`

) or ldiv (`\`

) operators are
first used and caches the type. The `matrix_type`

function can also be used to determine the type of the sparse matrix prior
to use of the div or ldiv operators. For example

a = tril (sprandn(1024, 1024, 0.02), -1) ... + speye(1024); matrix_type (a); ans = Lower

The result shows that Octave correctly determines the matrix type, a lower
triangular matrix. The function `matrix_type`

can also be used to force
the type of a matrix to a particular value. For example

a = matrix_type (tril (sprandn (1024, ... 1024, 0.02), -1) + speye(1024), 'Lower');

This allows the cost of determining the matrix type to be avoided. However, incorrectly defining the matrix type will result in incorrect results from solutions of linear equations, and so it is entirely the responsibility of the user to correctly identify the matrix type.

ISBN 095461206X | GNU Octave Manual Version 3 | See the print edition |