Description of sltrace2x2

Home > sltoolbox > smallmat > sltrace2x2.m

sltrace2x2

PURPOSE

SLTRACE2X2 Computes the trace of 2 x 2 matrices in a fast way

SYNOPSIS

function r = sltrace2x2(Ms)

DESCRIPTION

SLTRACE2X2 Computes the trace of 2 x 2 matrices in a fast way

 $ Syntax $
   - r = sltrace2x2(Ms)

 $ Arguments $
   - Ms:       the 2 x 2 matrix (matrices)
   - r:        the resultant trace(s)

 $ Description $
   - r = sltrace2x2(Ms) computes the trace of 2x2 matrices. If Ms is
     a 2 x 2 matrix, then r is a scalar representing its trace. 
     Or, if Ms is a 2 x 2 x ... array, then r would be a ... array 
     storing the trace of all 2 x 2 matrices.

 $ Remarks $
   - The function uses the following formula for fast calculation of
     trace of 2 x 2 matrices:
       det = a11 + a22

 $ History $
   - Created by Dahua Lin on Apr 22nd, 2006

CROSS-REFERENCE INFORMATION

This function calls:

This function is called by:

SOURCE CODE

0001 function r = sltrace2x2(Ms)
0002 %SLTRACE2X2 Computes the trace of 2 x 2 matrices in a fast way
0003 %
0004 % $ Syntax $
0005 %   - r = sltrace2x2(Ms)
0006 %
0007 % $ Arguments $
0008 %   - Ms:       the 2 x 2 matrix (matrices)
0009 %   - r:        the resultant trace(s)
0010 %
0011 % $ Description $
0012 %   - r = sltrace2x2(Ms) computes the trace of 2x2 matrices. If Ms is
0013 %     a 2 x 2 matrix, then r is a scalar representing its trace.
0014 %     Or, if Ms is a 2 x 2 x ... array, then r would be a ... array
0015 %     storing the trace of all 2 x 2 matrices.
0016 %
0017 % $ Remarks $
0018 %   - The function uses the following formula for fast calculation of
0019 %     trace of 2 x 2 matrices:
0020 %       det = a11 + a22
0021 %
0022 % $ History $
0023 %   - Created by Dahua Lin on Apr 22nd, 2006
0024 %
0025 
0026 %% parse and verify input arguments
0027 
0028 if size(Ms, 1) ~= 2 || size(Ms, 2) ~= 2
0029     error('sltoolbox:invalidarg', 'Ms should be set of 2 x 2 matrices');
0030 end
0031 
0032 %% compute
0033 
0034 if ndims(Ms) == 2       % single matrix
0035     r = Ms(1) + Ms(4);
0036     
0037 else                    % a set of matrices
0038     r = Ms(1,1,:) + Ms(2,2,:);
0039     
0040     siz = size(Ms);
0041     
0042     if ndims(Ms) == 3
0043         siz_r = [siz(3), 1];
0044     else
0045         siz_r = siz(3:end);
0046     end
0047     
0048     r = reshape(r, siz_r);
0049     
0050 end
0051

---

Generated on Wed 20-Sep-2006 12:43:11 by m2html © 2003