LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ cpptrs()

subroutine cpptrs ( character  UPLO,
integer  N,
integer  NRHS,
complex, dimension( * )  AP,
complex, dimension( ldb, * )  B,
integer  LDB,
integer  INFO 
)

CPPTRS

Download CPPTRS + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 CPPTRS solves a system of linear equations A*X = B with a Hermitian
 positive definite matrix A in packed storage using the Cholesky
 factorization A = U**H*U or A = L*L**H computed by CPPTRF.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
          = 'U':  Upper triangle of A is stored;
          = 'L':  Lower triangle of A is stored.
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in]NRHS
          NRHS is INTEGER
          The number of right hand sides, i.e., the number of columns
          of the matrix B.  NRHS >= 0.
[in]AP
          AP is COMPLEX array, dimension (N*(N+1)/2)
          The triangular factor U or L from the Cholesky factorization
          A = U**H*U or A = L*L**H, packed columnwise in a linear
          array.  The j-th column of U or L is stored in the array AP
          as follows:
          if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
[in,out]B
          B is COMPLEX array, dimension (LDB,NRHS)
          On entry, the right hand side matrix B.
          On exit, the solution matrix X.
[in]LDB
          LDB is INTEGER
          The leading dimension of the array B.  LDB >= max(1,N).
[out]INFO
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 107 of file cpptrs.f.

108 *
109 * -- LAPACK computational routine --
110 * -- LAPACK is a software package provided by Univ. of Tennessee, --
111 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
112 *
113 * .. Scalar Arguments ..
114  CHARACTER UPLO
115  INTEGER INFO, LDB, N, NRHS
116 * ..
117 * .. Array Arguments ..
118  COMPLEX AP( * ), B( LDB, * )
119 * ..
120 *
121 * =====================================================================
122 *
123 * .. Local Scalars ..
124  LOGICAL UPPER
125  INTEGER I
126 * ..
127 * .. External Functions ..
128  LOGICAL LSAME
129  EXTERNAL lsame
130 * ..
131 * .. External Subroutines ..
132  EXTERNAL ctpsv, xerbla
133 * ..
134 * .. Intrinsic Functions ..
135  INTRINSIC max
136 * ..
137 * .. Executable Statements ..
138 *
139 * Test the input parameters.
140 *
141  info = 0
142  upper = lsame( uplo, 'U' )
143  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
144  info = -1
145  ELSE IF( n.LT.0 ) THEN
146  info = -2
147  ELSE IF( nrhs.LT.0 ) THEN
148  info = -3
149  ELSE IF( ldb.LT.max( 1, n ) ) THEN
150  info = -6
151  END IF
152  IF( info.NE.0 ) THEN
153  CALL xerbla( 'CPPTRS', -info )
154  RETURN
155  END IF
156 *
157 * Quick return if possible
158 *
159  IF( n.EQ.0 .OR. nrhs.EQ.0 )
160  $ RETURN
161 *
162  IF( upper ) THEN
163 *
164 * Solve A*X = B where A = U**H * U.
165 *
166  DO 10 i = 1, nrhs
167 *
168 * Solve U**H *X = B, overwriting B with X.
169 *
170  CALL ctpsv( 'Upper', 'Conjugate transpose', 'Non-unit', n,
171  $ ap, b( 1, i ), 1 )
172 *
173 * Solve U*X = B, overwriting B with X.
174 *
175  CALL ctpsv( 'Upper', 'No transpose', 'Non-unit', n, ap,
176  $ b( 1, i ), 1 )
177  10 CONTINUE
178  ELSE
179 *
180 * Solve A*X = B where A = L * L**H.
181 *
182  DO 20 i = 1, nrhs
183 *
184 * Solve L*Y = B, overwriting B with X.
185 *
186  CALL ctpsv( 'Lower', 'No transpose', 'Non-unit', n, ap,
187  $ b( 1, i ), 1 )
188 *
189 * Solve L**H *X = Y, overwriting B with X.
190 *
191  CALL ctpsv( 'Lower', 'Conjugate transpose', 'Non-unit', n,
192  $ ap, b( 1, i ), 1 )
193  20 CONTINUE
194  END IF
195 *
196  RETURN
197 *
198 * End of CPPTRS
199 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine ctpsv(UPLO, TRANS, DIAG, N, AP, X, INCX)
CTPSV
Definition: ctpsv.f:144
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