W3C home > Mailing lists > Public > www-svg@w3.org > November 2007

The trouble with matrix multiplication « code monk

From: Karl Dubost <karl@w3.org>
Date: Wed, 21 Nov 2007 19:51:36 +0900
Message-Id: <D8776C3B-6764-4241-8DF6-7C01C7BF7B4A@w3.org>
To: www-svg@w3.org

For Information

     The trouble with matrix multiplication
2007-11-19

is that it’s not commutative. That means that when the SVG spec says  
in the documentation for the multiply method in the SVGMatrix DOM  
“this matrix is post-multiplied by another matrix” it really does  
matter which way round you do the multiplication of the two matrices.

In the call «A.multiply(B)», A is this and should be post-multiplied  
by B. In the usual mathematical convention the result should be AB.

Safari computes BA, Firefox computes AB. Oopsy.



     -- The trouble with matrix multiplication « code monk
     http://drj11.wordpress.com/2007/11/19/the-trouble-with-matrix-multiplication/
     Wed, 21 Nov 2007 10:50:19 GMT

--
Karl Dubost - W3C
http://www.w3.org/QA/
Be Strict To Be Cool
Received on Wednesday, 21 November 2007 10:51:49 GMT

This archive was generated by hypermail 2.3.1 : Friday, 8 March 2013 15:54:38 GMT