From: astroelectronic@t-online.de   
      
   Phil,   
      
   > Because you can't do that to a matrix.  Sorry, it's just linear   
   > algebra--if you do the calculation wrong, you'll get the wrong answer.   
   > I say that explicitly at the top of P. 206 (first edition).   
      
   ok, I accept that it doesn't work as expected, but I don't yet understand the   
   explanation.   
   If I multiply the Stokes vector for horizontal polarized light by a 90 degrees   
   rotation matrix, should the result be vertical polarized light? Or does that   
   also not work?   
      
   [1  0 0 0] * [1] = ?   
   [0  0 1 0]   [1]   
   [0 -1 0 0]   [0]   
   [0  0 0 1]   [0]   
      
   Rotation matrix from Gerrard/Burch: Introduction to Matrix Methods in Optics,   
   page 196   
   Stokes vector from https://en.wikipedia.org/wiki/Stokes_parameters   
      
   Michael   
      
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