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ZSYSV Example Program in Fortran
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* =============================================================================
*
* ZSYSV Example.
* ==============
*
* The program computes the solution to the system of linear equations
* with a complex symmetric matrix A and multiple right-hand sides B,
* where A is the coefficient matrix:
*
* ( 9.99, -4.73) ( -5.68, -0.80) ( -8.94, 1.32) ( -9.42, 2.05)
* ( -5.68, -0.80) ( -8.01, 4.61) ( 1.64, -6.29) ( 6.79, -2.17)
* ( -8.94, 1.32) ( 1.64, -6.29) ( 9.04, 3.96) ( -4.51, -7.54)
* ( -9.42, 2.05) ( 6.79, -2.17) ( -4.51, -7.54) ( 0.40, 4.06)
*
* and B is the right-hand side matrix:
*
* ( 5.71, -1.20) ( 2.84, -0.18)
* ( -7.70, 6.47) ( -8.29, -1.72)
* ( 3.77, -7.40) ( -4.28, -8.25)
* ( -3.78, 0.33) ( -2.70, -0.39)
*
* Description.
* ============
*
* The routine solves for X the complex system of linear equations A*X = B,
* where A is an n-by-n symmetric matrix, the columns of matrix B are
* individual right-hand sides, and the columns of X are the corresponding
* solutions.
*
* The diagonal pivoting method is used to factor A as A = U*D*UT or
* A = L*D*LT , where U (or L) is a product of permutation and unit upper
* (lower) triangular matrices, and D is symmetric and block diagonal with
* 1-by-1 and 2-by-2 diagonal blocks.
*
* The factored form of A is then used to solve the system of equations A*X = B.
*
* Example Program Results.
* ========================
*
* ZSYSV Example Program Results
*
* Solution
* ( 0.13, 0.13) ( 0.63, 0.34)
* ( 0.32, -0.07) ( 0.61, 0.21)
* ( -0.26, -0.44) ( -0.01, -0.10)
* ( -0.40, 0.51) ( 0.21, 0.02)
*
* Details of factorization
* (-16.42, 1.69) ( -0.53, 0.35) ( 0.36, 0.41) ( -0.78, 0.49)
* ( 0.00, 0.00) ( 3.69, 0.64) (-16.58, -1.61) ( -0.10, -0.65)
* ( 0.00, 0.00) ( 0.00, 0.00) ( 1.02, -3.74) ( -0.73, -0.52)
* ( 0.00, 0.00) ( 0.00, 0.00) ( 0.00, 0.00) ( 9.04, 3.96)
*
* Pivot indices
* 1 -1 -1 3
* =============================================================================
*
* .. Parameters ..
INTEGER N, NRHS
PARAMETER ( N = 4, NRHS = 2 )
INTEGER LDA, LDB
PARAMETER ( LDA = N, LDB = N )
INTEGER LWMAX
PARAMETER ( LWMAX = 100 )
*
* .. Local Scalars ..
INTEGER INFO, LWORK
*
* .. Local Arrays ..
INTEGER IPIV( N )
COMPLEX*16 A( LDA, N ), B( LDB, NRHS ), WORK( LWMAX )
DATA A/
$ ( 9.99,-4.73),( 0.00, 0.00),( 0.00, 0.00),( 0.00, 0.00),
$ (-5.68,-0.80),(-8.01, 4.61),( 0.00, 0.00),( 0.00, 0.00),
$ (-8.94, 1.32),( 1.64,-6.29),( 9.04, 3.96),( 0.00, 0.00),
$ (-9.42, 2.05),( 6.79,-2.17),(-4.51,-7.54),( 0.40, 4.06)
$ /
DATA B/
$ ( 5.71,-1.20),(-7.70, 6.47),( 3.77,-7.40),(-3.78, 0.33),
$ ( 2.84,-0.18),(-8.29,-1.72),(-4.28,-8.25),(-2.70,-0.39)
$ /
*
* .. External Subroutines ..
EXTERNAL ZSYSV
EXTERNAL PRINT_MATRIX, PRINT_INT_VECTOR
*
* .. Intrinsic Functions ..
INTRINSIC INT, MIN
*
* .. Executable Statements ..
WRITE(*,*)'ZSYSV Example Program Results'
*
* Query the optimal workspace.
*
LWORK = -1
CALL ZSYSV( 'Upper', N, NRHS, A, LDA, IPIV, B, LDB, WORK, LWORK,
$ INFO )
LWORK = MIN( LWMAX, INT( WORK( 1 ) ) )
*
* Solve the equations A*X = B.
*
CALL ZSYSV( 'Upper', N, NRHS, A, LDA, IPIV, B, LDB, WORK, LWORK,
$ INFO )
*
* Check for the exact singularity.
*
IF( INFO.GT.0 ) THEN
WRITE(*,*)'The element of the diagonal factor '
WRITE(*,*)'D(',INFO,',',INFO,') is zero, so that'
WRITE(*,*)'D is singular; the solution could not be computed.'
STOP
END IF
*
* Print solution.
*
CALL PRINT_MATRIX( 'Solution', N, NRHS, B, LDB )
*
* Print details of factorization.
*
CALL PRINT_MATRIX( 'Details of factorization', N, N, A, LDA )
*
* Print pivot indices.
*
CALL PRINT_INT_VECTOR( 'Pivot indices', N, IPIV )
STOP
END
*
* End of ZSYSV Example.
*
* =============================================================================
*
* Auxiliary routine: printing a matrix.
*
SUBROUTINE PRINT_MATRIX( DESC, M, N, A, LDA )
CHARACTER*(*) DESC
INTEGER M, N, LDA
COMPLEX*16 A( LDA, * )
*
INTEGER I, J
*
WRITE(*,*)
WRITE(*,*) DESC
DO I = 1, M
WRITE(*,9998) ( A( I, J ), J = 1, N )
END DO
*
9998 FORMAT( 11(:,1X,'(',F6.2,',',F6.2,')') )
RETURN
END
*
* Auxiliary routine: printing a vector of integers.
*
SUBROUTINE PRINT_INT_VECTOR( DESC, N, A )
CHARACTER*(*) DESC
INTEGER N
INTEGER A( N )
*
INTEGER I
*
WRITE(*,*)
WRITE(*,*) DESC
WRITE(*,9999) ( A( I ), I = 1, N )
*
9999 FORMAT( 11(:,1X,I6) )
RETURN
END
Parent topic: ZSYSV Example