From: ruby-core@...
Date: 2015-02-23T16:38:55+00:00
Subject: [ruby-core:68265] [Ruby trunk - Bug #10855] [PATCH] Matrix#inverse returns matrix of integers whenever possible

Issue #10855 has been updated by Marc-Andre Lafortune.


TBH, I can't think of any legitimate use of `Matrix#/` with integer division.  Anyone?

I never really thought of that, but it's a bit odd that there is no natural way to write `Matrix.I(3) / 2`, say. There's no `quo` method on `Matrix`, so one has to do `Matrix.I(3) / 2r`, `Matrix.I(3) * 0.5r` or `Matrix.diagonal([0.5r] * 3)`.

I'm very tempted to change `/` to act like `quo`.

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Bug #10855: [PATCH] Matrix#inverse returns matrix of integers whenever possible
https://bugs.ruby-lang.org/issues/10855#change-51620

* Author: Lito Nicolai
* Status: Open
* Priority: Normal
* Assignee: Marc-Andre Lafortune
* ruby -v: 2.3.0
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
Currently, Matrix#inverse returns a matrix of Rationals, even when each
element has a denominator of 1. This leads to 

	> x = Matrix.identity 3
	=> Matrix[[1, 0, 0],
                  [0, 1, 0],
                  [0, 0, 1]]

	> x.inverse
	=> Matrix[[(1/1), (0/1), (0/1)],
		  [(0/1), (1/1), (0/1)],
                  [(0/1), (0/1), (1/1)]]

Even though `Matrix.identity.inverse` should be identical to `Matrix.identity`.

This patch guarantees that Matrix#inverse will return a matrix of integers
whenever it can. To maintain uniform types across a matrix, the conversion 
is only performedif *every* element can be converted to an integer.

---Files--------------------------------
matrix_inverse_to_integer.patch (2.14 KB)


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