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authorjason <jason@8a072113-8704-0410-8d35-dd094bca7971>2008-10-28 01:38:50 +0000
committerjason <jason@8a072113-8704-0410-8d35-dd094bca7971>2008-10-28 01:38:50 +0000
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+ SUBROUTINE CPPT01( UPLO, N, A, AFAC, RWORK, RESID )
+*
+* -- LAPACK test routine (version 3.1) --
+* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
+* November 2006
+*
+* .. Scalar Arguments ..
+ CHARACTER UPLO
+ INTEGER N
+ REAL RESID
+* ..
+* .. Array Arguments ..
+ REAL RWORK( * )
+ COMPLEX A( * ), AFAC( * )
+* ..
+*
+* Purpose
+* =======
+*
+* CPPT01 reconstructs a Hermitian positive definite packed matrix A
+* from its L*L' or U'*U factorization and computes the residual
+* norm( L*L' - A ) / ( N * norm(A) * EPS ) or
+* norm( U'*U - A ) / ( N * norm(A) * EPS ),
+* where EPS is the machine epsilon, L' is the conjugate transpose of
+* L, and U' is the conjugate transpose of U.
+*
+* Arguments
+* ==========
+*
+* UPLO (input) CHARACTER*1
+* Specifies whether the upper or lower triangular part of the
+* Hermitian 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 Hermitian matrix A, stored as a packed
+* triangular matrix.
+*
+* AFAC (input/output) COMPLEX array, dimension (N*(N+1)/2)
+* On entry, the factor L or U from the L*L' or U'*U
+* factorization of A, stored as a packed triangular matrix.
+* Overwritten with the reconstructed matrix, and then with the
+* difference L*L' - A (or U'*U - A).
+*
+* RWORK (workspace) REAL array, dimension (N)
+*
+* RESID (output) REAL
+* If UPLO = 'L', norm(L*L' - A) / ( N * norm(A) * EPS )
+* If UPLO = 'U', norm(U'*U - A) / ( N * norm(A) * EPS )
+*
+* =====================================================================
+*
+* .. Parameters ..
+ REAL ZERO, ONE
+ PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
+* ..
+* .. Local Scalars ..
+ INTEGER I, K, KC
+ REAL ANORM, EPS, TR
+ COMPLEX TC
+* ..
+* .. External Functions ..
+ LOGICAL LSAME
+ REAL CLANHP, SLAMCH
+ COMPLEX CDOTC
+ EXTERNAL LSAME, CLANHP, SLAMCH, CDOTC
+* ..
+* .. External Subroutines ..
+ EXTERNAL CHPR, CSCAL, CTPMV
+* ..
+* .. Intrinsic Functions ..
+ INTRINSIC AIMAG, REAL
+* ..
+* .. Executable Statements ..
+*
+* Quick exit if N = 0
+*
+ IF( N.LE.0 ) THEN
+ RESID = ZERO
+ RETURN
+ END IF
+*
+* Exit with RESID = 1/EPS if ANORM = 0.
+*
+ EPS = SLAMCH( 'Epsilon' )
+ ANORM = CLANHP( '1', UPLO, N, A, RWORK )
+ IF( ANORM.LE.ZERO ) THEN
+ RESID = ONE / EPS
+ RETURN
+ END IF
+*
+* Check the imaginary parts of the diagonal elements and return with
+* an error code if any are nonzero.
+*
+ KC = 1
+ IF( LSAME( UPLO, 'U' ) ) THEN
+ DO 10 K = 1, N
+ IF( AIMAG( AFAC( KC ) ).NE.ZERO ) THEN
+ RESID = ONE / EPS
+ RETURN
+ END IF
+ KC = KC + K + 1
+ 10 CONTINUE
+ ELSE
+ DO 20 K = 1, N
+ IF( AIMAG( AFAC( KC ) ).NE.ZERO ) THEN
+ RESID = ONE / EPS
+ RETURN
+ END IF
+ KC = KC + N - K + 1
+ 20 CONTINUE
+ END IF
+*
+* Compute the product U'*U, overwriting U.
+*
+ IF( LSAME( UPLO, 'U' ) ) THEN
+ KC = ( N*( N-1 ) ) / 2 + 1
+ DO 30 K = N, 1, -1
+*
+* Compute the (K,K) element of the result.
+*
+ TR = CDOTC( K, AFAC( KC ), 1, AFAC( KC ), 1 )
+ AFAC( KC+K-1 ) = TR
+*
+* Compute the rest of column K.
+*
+ IF( K.GT.1 ) THEN
+ CALL CTPMV( 'Upper', 'Conjugate', 'Non-unit', K-1, AFAC,
+ $ AFAC( KC ), 1 )
+ KC = KC - ( K-1 )
+ END IF
+ 30 CONTINUE
+*
+* Compute the difference L*L' - A
+*
+ KC = 1
+ DO 50 K = 1, N
+ DO 40 I = 1, K - 1
+ AFAC( KC+I-1 ) = AFAC( KC+I-1 ) - A( KC+I-1 )
+ 40 CONTINUE
+ AFAC( KC+K-1 ) = AFAC( KC+K-1 ) - REAL( A( KC+K-1 ) )
+ KC = KC + K
+ 50 CONTINUE
+*
+* Compute the product L*L', overwriting L.
+*
+ ELSE
+ KC = ( N*( N+1 ) ) / 2
+ DO 60 K = N, 1, -1
+*
+* Add a multiple of column K of the factor L to each of
+* columns K+1 through N.
+*
+ IF( K.LT.N )
+ $ CALL CHPR( 'Lower', N-K, ONE, AFAC( KC+1 ), 1,
+ $ AFAC( KC+N-K+1 ) )
+*
+* Scale column K by the diagonal element.
+*
+ TC = AFAC( KC )
+ CALL CSCAL( N-K+1, TC, AFAC( KC ), 1 )
+*
+ KC = KC - ( N-K+2 )
+ 60 CONTINUE
+*
+* Compute the difference U'*U - A
+*
+ KC = 1
+ DO 80 K = 1, N
+ AFAC( KC ) = AFAC( KC ) - REAL( A( KC ) )
+ DO 70 I = K + 1, N
+ AFAC( KC+I-K ) = AFAC( KC+I-K ) - A( KC+I-K )
+ 70 CONTINUE
+ KC = KC + N - K + 1
+ 80 CONTINUE
+ END IF
+*
+* Compute norm( L*U - A ) / ( N * norm(A) * EPS )
+*
+ RESID = CLANHP( '1', UPLO, N, AFAC, RWORK )
+*
+ RESID = ( ( RESID / REAL( N ) ) / ANORM ) / EPS
+*
+ RETURN
+*
+* End of CPPT01
+*
+ END