Hi,

Is there a built in function that can get the sum of the upper secondary diagonals of a matrix? some times called the skew:



I can call each by its element, but I would like it to work for any a1n & an1, I can do tr(reverse) to find the secondary diagonal, after each reduction of the matrix by 1 row/column:



matrix multiplier.sm (16kb) downloaded 10 time(s).

Thanks in advance
Ian

Hello

Maybe you can do this




Best Regards

Carlos

Hi Jean,

The image was just to illustrate the direction of the summation, the primary diagonal is top left to bottom right.

Hi Carlos and Davide,

These look like interesting solutions, let me try on the larger matrix.

Thanks once again
Ian

You should try the 2nd method in my file.
As stated in the previous post the first method is really inefficient, since for each iteration it calculates all the sums from the first value up to the n-th diagonal.

BTW with a random set of values and small matrices, doesn't seems so slow in my machine (WIN7PRO/AMD PRO A10/16GB RAM). With bigger matrices the difference is huge (for a 100x100 matrix, 26.1s with first method, 0.028s with second method)





The method to check the sum of [r,c] coordinates can be used more efficently in a double loop, though (here it is extended to the whole matrix).

Edited by user 03 December 2021 15:38:35(UTC)  | Reason: Not specified

w/o abstract: of little interest for common visitor.

Matrix DIAGONAL.sm (12kb) downloaded 10 time(s).