HP 41C matrix editor and extend memory

[Les Bell]

(08-11-2015 12:03 AM)mbrethen Wrote:  Does anyone know what file type is created?

According to p. 33 of the manual, "A matrix in extended memory has a file length of m x n (2m x 2n for a complex matrix). Its file type is unique to matrices. Do not use the function [CLFL] with a matrix in extended memory: this destroys part of the file's header information. Instead, use [PURFL] to purge the entire matrix".

The [EMDIR] function just shows the file type as "@" rather than "D" for a data file. It shows the size as being (m x n) as you'd expect, though, i.e. a 4 x 4 matrix is shown as 16 registers.

I presume the unique file type is due to the fact that the ROM often transforms the matrix into an LU (lower-upper) decomposition (e.g. when solving a system of equations or calculating a determinant). The LU decomposition form "is an unrecognizably altered form of a matrix, often containing Alpha data" (p. 52 of the manual). There are lots of dire warnings in that part of the manual.