Antonio --

Valentin is, of course, correct. The "--" indicates that the matrix has been replaced by an *encoded* form of an LU decomposition, which takes no more space than the original matrix.

Linear-system solutions are often computed much more quickly using the LU decomposition of the original matrix. This is useful when computing multiple linear-system solutions using the same system matrix. The determinant of an LU matrix is trivially simple to compute.

When solving a system of equations, the original matrix is replaced by the encoded LU decomposition. However, when calculating the determinant of a matrix, the encoded LU decomposition is stored to the RESULT matrix. This will increase the amount of matrix storage space required, unless the identifier of the RESULT matrix is the same as that of the original matrix. Users should keep this in mind if an attempt to calculate the determinant produces a puzzling "Error 10" message (not enough free memory).

More-detailed information about the LU decomposition as implemented in the HP-15C can be found in Section 4 of the HP-15C Advanced Functions Handbook. A scan of this manual is available on the MoHPC CD- and DVD-ROM sets.

Regards,

-- KS

*Edited: 25 Apr 2006, 3:14 a.m. *