CREATEROTATION90  Matrix of a rotation for 90 degrees multiples.

   MAT = createRotation90
   Returns the 3-by-3 matrix corresponding to a rotation by 90 degrees.
   As trigonometric functions are explicitley converted to +1 or -1, the
   resulting matrix obtained with this function is more precise than 
   the one obtained with createRotation.

   MAT = createRotation90(NUM)
   Specifies the number of rotations to performs. NUM should be an integer
   (possibly negative).

   Example
     poly = [10 0;20 0;10 10];
     rot = createRotation90;
     poly2 = transformPoint(poly, rot);
     figure; hold on; axis equal;
     drawPolygon(poly);
     drawPolygon(poly2, 'm');
     legend('original', 'rotated');

     % specify number of rotations, and center
     rot = createRotation90(2, [10 10]);
     poly3 = transformPoint(poly, rot);
     drawPolygon(poly3, 'g');

   See also
   transforms2d, createRotation

 ------
 Author: David Legland
 e-mail: david.legland@grignon.inra.fr
 Created: 2012-06-20,    using Matlab 7.9.0.529 (R2009b)
 Copyright 2012 INRA - Cepia Software Platform.

Package: matgeom