matrix-cos-angle

[bdeket]

possible fix for #117

• prevent zero-matrix in test
• better error on zero-matrix

but I'm not sure if the error/nan-branch is the best way to go about it.

[soegaard]

How does an error message look like, when the error condition is triggered?

Maybe raise-arguments-error could be used to give a nicer error message?

[pavpanchekha]

This is fine but I imagine the point of the original code is to produce a matrix with infinities or NaNs in it, possibly of the correct sign.

[bdeket]

• raise-argument(s)-error: I tried this first, but since the docs don't mention anything about non-zero matrices I found the "contract violation" part of the error message incorrect. So I ended up writing an error in the style of "/: division by zero". But then it should complain about "zero matrix" and not "non-zero matrix" as I have done: I will push an update to get the error mentioned below.
• nan's: This code only produces 1 number, I tried to keep it the same as before (racket 8.14) Looking at it again it's not completely the same:

#lang racket/base
(require math)
                                                                 ;; 8.14         now (and 9.1)
(matrix-cos-angle (matrix [[0 1]]) (matrix [[0.0 0.0]]))         ;; nan          nan
(matrix-cos-angle (matrix [[0.0 1]]) (matrix [[0 0.0]]))         ;; nan          nan
(matrix-cos-angle (matrix [[0 1]]) (matrix [[0.0 0]]))           ;; 0            0
(matrix-cos-angle (matrix [[0 1]]) (matrix [[+nan.0 0]]))        ;; 0            0
(matrix-cos-angle (matrix [[1 1]]) (matrix [[+nan.0 0]]))        ;; nan          nan
(matrix-cos-angle (matrix [[0+1i 1]]) (matrix [[+nan.0 0]]))     ;; 0+nani       nan+nani <<<<
(matrix-cos-angle (matrix [[0.+1i 1]]) (matrix [[+nan.0 0]]))    ;; nan+nani     nan+nani
(matrix-cos-angle (matrix [[1 1]]) (matrix [[+nan.0+1i 0]]))     ;; nan+nani     nan+nani
(matrix-cos-angle (matrix [[0+1i 1]]) (matrix [[+nan.0+1i 0]]))  ;; nan+nani     nan+nani
(matrix-cos-angle (matrix [[1+0i 1]]) (matrix [[0+nan.0i 0]]))   ;; 0+nani       nan+nani <<<<
(matrix-cos-angle (matrix [[1+0.i 1]]) (matrix [[0+nan.0i 0]]))  ;; nan+nani     nan+nani
(matrix-cos-angle (matrix [[1+0i 1]]) (matrix [[0 0]]))          ;; error        error (= "matrix-cos-angle: zero matrix #<array #(1 2) #[0 0]>")