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SUBROUTINE CSPT03( UPLO, N, A, AINV, WORK, LDW, RWORK, RCOND,
$ RESID )
*
* -- LAPACK test routine (version 3.0) --
* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
* Courant Institute, Argonne National Lab, and Rice University
* February 29, 1992
*
* .. Scalar Arguments ..
CHARACTER UPLO
INTEGER LDW, N
REAL RCOND, RESID
* ..
* .. Array Arguments ..
REAL RWORK( * )
COMPLEX A( * ), AINV( * ), WORK( LDW, * )
* ..
*
* Purpose
* =======
*
* CSPT03 computes the residual for a complex symmetric packed matrix
* times its inverse:
* norm( I - A*AINV ) / ( N * norm(A) * norm(AINV) * EPS ),
* where EPS is the machine epsilon.
*
* Arguments
* ==========
*
* UPLO (input) CHARACTER*1
* Specifies whether the upper or lower triangular part of the
* complex symmetric matrix A is stored:
* = 'U': Upper triangular
* = 'L': Lower triangular
*
* N (input) INTEGER
* The number of rows and columns of the matrix A. N >= 0.
*
* A (input) COMPLEX array, dimension (N*(N+1)/2)
* The original complex symmetric matrix A, stored as a packed
* triangular matrix.
*
* AINV (input) COMPLEX array, dimension (N*(N+1)/2)
* The (symmetric) inverse of the matrix A, stored as a packed
* triangular matrix.
*
* WORK (workspace) COMPLEX array, dimension (LDWORK,N)
*
* LDWORK (input) INTEGER
* The leading dimension of the array WORK. LDWORK >= max(1,N).
*
* RWORK (workspace) REAL array, dimension (N)
*
* RCOND (output) REAL
* The reciprocal of the condition number of A, computed as
* ( 1/norm(A) ) / norm(AINV).
*
* RESID (output) REAL
* norm(I - A*AINV) / ( N * norm(A) * norm(AINV) * EPS )
*
* =====================================================================
*
* .. Parameters ..
REAL ZERO, ONE
PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
* ..
* .. Local Scalars ..
INTEGER I, ICOL, J, JCOL, K, KCOL, NALL
REAL AINVNM, ANORM, EPS
COMPLEX T
* ..
* .. External Functions ..
LOGICAL LSAME
REAL CLANGE, CLANSP, SLAMCH
COMPLEX CDOTU
EXTERNAL LSAME, CLANGE, CLANSP, SLAMCH, CDOTU
* ..
* .. Intrinsic Functions ..
INTRINSIC REAL
* ..
* .. Executable Statements ..
*
* Quick exit if N = 0.
*
IF( N.LE.0 ) THEN
RCOND = ONE
RESID = ZERO
RETURN
END IF
*
* Exit with RESID = 1/EPS if ANORM = 0 or AINVNM = 0.
*
EPS = SLAMCH( 'Epsilon' )
ANORM = CLANSP( '1', UPLO, N, A, RWORK )
AINVNM = CLANSP( '1', UPLO, N, AINV, RWORK )
IF( ANORM.LE.ZERO .OR. AINVNM.LE.ZERO ) THEN
RCOND = ZERO
RESID = ONE / EPS
RETURN
END IF
RCOND = ( ONE/ANORM ) / AINVNM
*
* Case where both A and AINV are upper triangular:
* Each element of - A * AINV is computed by taking the dot product
* of a row of A with a column of AINV.
*
IF( LSAME( UPLO, 'U' ) ) THEN
DO 70 I = 1, N
ICOL = ( ( I-1 )*I ) / 2 + 1
*
* Code when J <= I
*
DO 30 J = 1, I
JCOL = ( ( J-1 )*J ) / 2 + 1
T = CDOTU( J, A( ICOL ), 1, AINV( JCOL ), 1 )
JCOL = JCOL + 2*J - 1
KCOL = ICOL - 1
DO 10 K = J + 1, I
T = T + A( KCOL+K )*AINV( JCOL )
JCOL = JCOL + K
10 CONTINUE
KCOL = KCOL + 2*I
DO 20 K = I + 1, N
T = T + A( KCOL )*AINV( JCOL )
KCOL = KCOL + K
JCOL = JCOL + K
20 CONTINUE
WORK( I, J ) = -T
30 CONTINUE
*
* Code when J > I
*
DO 60 J = I + 1, N
JCOL = ( ( J-1 )*J ) / 2 + 1
T = CDOTU( I, A( ICOL ), 1, AINV( JCOL ), 1 )
JCOL = JCOL - 1
KCOL = ICOL + 2*I - 1
DO 40 K = I + 1, J
T = T + A( KCOL )*AINV( JCOL+K )
KCOL = KCOL + K
40 CONTINUE
JCOL = JCOL + 2*J
DO 50 K = J + 1, N
T = T + A( KCOL )*AINV( JCOL )
KCOL = KCOL + K
JCOL = JCOL + K
50 CONTINUE
WORK( I, J ) = -T
60 CONTINUE
70 CONTINUE
ELSE
*
* Case where both A and AINV are lower triangular
*
NALL = ( N*( N+1 ) ) / 2
DO 140 I = 1, N
*
* Code when J <= I
*
ICOL = NALL - ( ( N-I+1 )*( N-I+2 ) ) / 2 + 1
DO 100 J = 1, I
JCOL = NALL - ( ( N-J )*( N-J+1 ) ) / 2 - ( N-I )
T = CDOTU( N-I+1, A( ICOL ), 1, AINV( JCOL ), 1 )
KCOL = I
JCOL = J
DO 80 K = 1, J - 1
T = T + A( KCOL )*AINV( JCOL )
JCOL = JCOL + N - K
KCOL = KCOL + N - K
80 CONTINUE
JCOL = JCOL - J
DO 90 K = J, I - 1
T = T + A( KCOL )*AINV( JCOL+K )
KCOL = KCOL + N - K
90 CONTINUE
WORK( I, J ) = -T
100 CONTINUE
*
* Code when J > I
*
ICOL = NALL - ( ( N-I )*( N-I+1 ) ) / 2
DO 130 J = I + 1, N
JCOL = NALL - ( ( N-J+1 )*( N-J+2 ) ) / 2 + 1
T = CDOTU( N-J+1, A( ICOL-N+J ), 1, AINV( JCOL ), 1 )
KCOL = I
JCOL = J
DO 110 K = 1, I - 1
T = T + A( KCOL )*AINV( JCOL )
JCOL = JCOL + N - K
KCOL = KCOL + N - K
110 CONTINUE
KCOL = KCOL - I
DO 120 K = I, J - 1
T = T + A( KCOL+K )*AINV( JCOL )
JCOL = JCOL + N - K
120 CONTINUE
WORK( I, J ) = -T
130 CONTINUE
140 CONTINUE
END IF
*
* Add the identity matrix to WORK .
*
DO 150 I = 1, N
WORK( I, I ) = WORK( I, I ) + ONE
150 CONTINUE
*
* Compute norm(I - A*AINV) / (N * norm(A) * norm(AINV) * EPS)
*
RESID = CLANGE( '1', N, N, WORK, LDW, RWORK )
*
RESID = ( ( RESID*RCOND )/EPS ) / REAL( N )
*
RETURN
*
* End of CSPT03
*
END
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