mirror of https://gitlab.com/QEF/q-e.git
50 lines
1.5 KiB
Fortran
50 lines
1.5 KiB
Fortran
!
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! Copyright (C) 2004 PWSCF-CP-FPMD group
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! This file is distributed under the terms of the
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! GNU General Public License. See the file `License'
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! in the root directory of the present distribution,
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! or http://www.gnu.org/copyleft/gpl.txt .
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!
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#include "f_defs.h"
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!
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subroutine invmat (n, a, a_inv, da)
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!-----------------------------------------------------------------------
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! computes the inverse "a_inv" of matrix "a", both dimensioned (n,n)
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! if the matrix is dimensioned 3x3, it also computes determinant "da"
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! matrix "a" is unchanged on output - LAPACK
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!
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USE kinds
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implicit none
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integer :: n
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real(kind=DP), DIMENSION (n,n) :: a, a_inv
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real(kind=DP) :: da
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!
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integer :: info, lda, lwork, ipiv (n)
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! info=0: inversion was successful
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! lda : leading dimension (the same as n)
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! ipiv : work space for pivoting (assumed of length lwork=n)
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real(kind=DP) :: work (n)
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! more work space
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!
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lda = n
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lwork=n
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!
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a_inv(:,:) = a(:,:)
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!
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call DGETRF (n, n, a_inv, lda, ipiv, info)
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call errore ('invmat', 'error in DGETRF', abs (info) )
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call DGETRI (n, a_inv, lda, ipiv, work, lwork, info)
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call errore ('invmat', 'error in DGETRI', abs (info) )
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!
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if (n == 3) then
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da = a(1,1)*(a(2,2)*a(3,3)-a(2,3)*a(3,2)) + &
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a(1,2)*(a(2,3)*a(3,1)-a(2,1)*a(3,3)) + &
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a(1,3)*(a(2,1)*a(3,2)-a(3,1)*a(2,2))
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IF (ABS(da) < 1.d-10) CALL errore(' invmat ',' singular matrix ', 1)
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else
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da = 0.d0
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end if
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return
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end subroutine invmat
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