Added some clarifying comments to the svd function.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402306

dlib/matrix/matrix_utilities_abstract.h

@@ -546,6 +546,9 @@ namespace dlib
             - m == #u*#w*trans(#v)
             - trans(#u)*#u == identity matrix
             - trans(#v)*#v == identity matrix
+            - diag(#w) == the eigenvalues of the matrix m in no 
+              particular order.  All non-diagonal elements of #w are
+              set to 0.
             - #u.nr() == m.nr()
             - #u.nc() == m.nc()
             - #w.nr() == m.nc()