// 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