LAPACK 3.3.0

cpptrs.f

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```00001       SUBROUTINE CPPTRS( UPLO, N, NRHS, AP, B, LDB, INFO )
00002 *
00003 *  -- LAPACK routine (version 3.2) --
00004 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00005 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00006 *     November 2006
00007 *
00008 *     .. Scalar Arguments ..
00009       CHARACTER          UPLO
00010       INTEGER            INFO, LDB, N, NRHS
00011 *     ..
00012 *     .. Array Arguments ..
00013       COMPLEX            AP( * ), B( LDB, * )
00014 *     ..
00015 *
00016 *  Purpose
00017 *  =======
00018 *
00019 *  CPPTRS solves a system of linear equations A*X = B with a Hermitian
00020 *  positive definite matrix A in packed storage using the Cholesky
00021 *  factorization A = U**H*U or A = L*L**H computed by CPPTRF.
00022 *
00023 *  Arguments
00024 *  =========
00025 *
00026 *  UPLO    (input) CHARACTER*1
00027 *          = 'U':  Upper triangle of A is stored;
00028 *          = 'L':  Lower triangle of A is stored.
00029 *
00030 *  N       (input) INTEGER
00031 *          The order of the matrix A.  N >= 0.
00032 *
00033 *  NRHS    (input) INTEGER
00034 *          The number of right hand sides, i.e., the number of columns
00035 *          of the matrix B.  NRHS >= 0.
00036 *
00037 *  AP      (input) COMPLEX array, dimension (N*(N+1)/2)
00038 *          The triangular factor U or L from the Cholesky factorization
00039 *          A = U**H*U or A = L*L**H, packed columnwise in a linear
00040 *          array.  The j-th column of U or L is stored in the array AP
00041 *          as follows:
00042 *          if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
00043 *          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
00044 *
00045 *  B       (input/output) COMPLEX array, dimension (LDB,NRHS)
00046 *          On entry, the right hand side matrix B.
00047 *          On exit, the solution matrix X.
00048 *
00049 *  LDB     (input) INTEGER
00050 *          The leading dimension of the array B.  LDB >= max(1,N).
00051 *
00052 *  INFO    (output) INTEGER
00053 *          = 0:  successful exit
00054 *          < 0:  if INFO = -i, the i-th argument had an illegal value
00055 *
00056 *  =====================================================================
00057 *
00058 *     .. Local Scalars ..
00059       LOGICAL            UPPER
00060       INTEGER            I
00061 *     ..
00062 *     .. External Functions ..
00063       LOGICAL            LSAME
00064       EXTERNAL           LSAME
00065 *     ..
00066 *     .. External Subroutines ..
00067       EXTERNAL           CTPSV, XERBLA
00068 *     ..
00069 *     .. Intrinsic Functions ..
00070       INTRINSIC          MAX
00071 *     ..
00072 *     .. Executable Statements ..
00073 *
00074 *     Test the input parameters.
00075 *
00076       INFO = 0
00077       UPPER = LSAME( UPLO, 'U' )
00078       IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
00079          INFO = -1
00080       ELSE IF( N.LT.0 ) THEN
00081          INFO = -2
00082       ELSE IF( NRHS.LT.0 ) THEN
00083          INFO = -3
00084       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
00085          INFO = -6
00086       END IF
00087       IF( INFO.NE.0 ) THEN
00088          CALL XERBLA( 'CPPTRS', -INFO )
00089          RETURN
00090       END IF
00091 *
00092 *     Quick return if possible
00093 *
00094       IF( N.EQ.0 .OR. NRHS.EQ.0 )
00095      \$   RETURN
00096 *
00097       IF( UPPER ) THEN
00098 *
00099 *        Solve A*X = B where A = U'*U.
00100 *
00101          DO 10 I = 1, NRHS
00102 *
00103 *           Solve U'*X = B, overwriting B with X.
00104 *
00105             CALL CTPSV( 'Upper', 'Conjugate transpose', 'Non-unit', N,
00106      \$                  AP, B( 1, I ), 1 )
00107 *
00108 *           Solve U*X = B, overwriting B with X.
00109 *
00110             CALL CTPSV( 'Upper', 'No transpose', 'Non-unit', N, AP,
00111      \$                  B( 1, I ), 1 )
00112    10    CONTINUE
00113       ELSE
00114 *
00115 *        Solve A*X = B where A = L*L'.
00116 *
00117          DO 20 I = 1, NRHS
00118 *
00119 *           Solve L*Y = B, overwriting B with X.
00120 *
00121             CALL CTPSV( 'Lower', 'No transpose', 'Non-unit', N, AP,
00122      \$                  B( 1, I ), 1 )
00123 *
00124 *           Solve L'*X = Y, overwriting B with X.
00125 *
00126             CALL CTPSV( 'Lower', 'Conjugate transpose', 'Non-unit', N,
00127      \$                  AP, B( 1, I ), 1 )
00128    20    CONTINUE
00129       END IF
00130 *
00131       RETURN
00132 *
00133 *     End of CPPTRS
00134 *
00135       END
```