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// Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
// Copyright (C) INRIA
// Copyright (C) DIGITEO - 2011 - Allan CORNET
//
// This file must be used under the terms of the CeCILL.
// This source file is licensed as described in the file COPYING, which
// you should have received as part of this distribution. The terms
// are also available at
// http://www.cecill.info/licences/Licence_CeCILL_V2.1-en.txt
function x = signm(a)
// signm - computes the matrix sign function.
//%CALLING SEQUENCE
// x=signm(a)
//%PARAMETERS
// a : square hermitian matrix
// x : square hermitian matrix
//%DESCRIPTION
// This macro is called by the function sign to compute square matrix
// sign function.
rhs = argn(2);
if rhs <> 1 then
error(msprintf(gettext("%s: Wrong number of input argument(s): %d expected.\n"),"signm", 1));
end
[m, n] = size(a);
if m <> n then
error(msprintf(gettext("%s: Wrong size for input argument #%d: Square matrix expected.\n"),"signm",1));
end
flag = or(a <> a');
if flag then
error(msprintf(gettext("%s: Wrong value for input argument #%d: Non-hermitian matrix.\n"),"signm",1));
end
[u, s] = schur(a);
x = u'*diag(sign(real(diag(s)))) * u;
endfunction
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