 LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
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## ◆ zpotrs()

 subroutine zpotrs ( character UPLO, integer N, integer NRHS, complex*16, dimension( lda, * ) A, integer LDA, complex*16, dimension( ldb, * ) B, integer LDB, integer INFO )

ZPOTRS

Purpose:
``` ZPOTRS solves a system of linear equations A*X = B with a Hermitian
positive definite matrix A using the Cholesky factorization
A = U**H * U or A = L * L**H computed by ZPOTRF.```
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] A ``` A is COMPLEX*16 array, dimension (LDA,N) The triangular factor U or L from the Cholesky factorization A = U**H * U or A = L * L**H, as computed by ZPOTRF.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).``` [in,out] B ``` B is COMPLEX*16 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```

Definition at line 109 of file zpotrs.f.

110*
111* -- LAPACK computational routine --
112* -- LAPACK is a software package provided by Univ. of Tennessee, --
113* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
114*
115* .. Scalar Arguments ..
116 CHARACTER UPLO
117 INTEGER INFO, LDA, LDB, N, NRHS
118* ..
119* .. Array Arguments ..
120 COMPLEX*16 A( LDA, * ), B( LDB, * )
121* ..
122*
123* =====================================================================
124*
125* .. Parameters ..
126 COMPLEX*16 ONE
127 parameter( one = ( 1.0d+0, 0.0d+0 ) )
128* ..
129* .. Local Scalars ..
130 LOGICAL UPPER
131* ..
132* .. External Functions ..
133 LOGICAL LSAME
134 EXTERNAL lsame
135* ..
136* .. External Subroutines ..
137 EXTERNAL xerbla, ztrsm
138* ..
139* .. Intrinsic Functions ..
140 INTRINSIC max
141* ..
142* .. Executable Statements ..
143*
144* Test the input parameters.
145*
146 info = 0
147 upper = lsame( uplo, 'U' )
148 IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
149 info = -1
150 ELSE IF( n.LT.0 ) THEN
151 info = -2
152 ELSE IF( nrhs.LT.0 ) THEN
153 info = -3
154 ELSE IF( lda.LT.max( 1, n ) ) THEN
155 info = -5
156 ELSE IF( ldb.LT.max( 1, n ) ) THEN
157 info = -7
158 END IF
159 IF( info.NE.0 ) THEN
160 CALL xerbla( 'ZPOTRS', -info )
161 RETURN
162 END IF
163*
164* Quick return if possible
165*
166 IF( n.EQ.0 .OR. nrhs.EQ.0 )
167 \$ RETURN
168*
169 IF( upper ) THEN
170*
171* Solve A*X = B where A = U**H *U.
172*
173* Solve U**H *X = B, overwriting B with X.
174*
175 CALL ztrsm( 'Left', 'Upper', 'Conjugate transpose', 'Non-unit',
176 \$ n, nrhs, one, a, lda, b, ldb )
177*
178* Solve U*X = B, overwriting B with X.
179*
180 CALL ztrsm( 'Left', 'Upper', 'No transpose', 'Non-unit', n,
181 \$ nrhs, one, a, lda, b, ldb )
182 ELSE
183*
184* Solve A*X = B where A = L*L**H.
185*
186* Solve L*X = B, overwriting B with X.
187*
188 CALL ztrsm( 'Left', 'Lower', 'No transpose', 'Non-unit', n,
189 \$ nrhs, one, a, lda, b, ldb )
190*
191* Solve L**H *X = B, overwriting B with X.
192*
193 CALL ztrsm( 'Left', 'Lower', 'Conjugate transpose', 'Non-unit',
194 \$ n, nrhs, one, a, lda, b, ldb )
195 END IF
196*
197 RETURN
198*
199* End of ZPOTRS
200*
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine ztrsm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
ZTRSM
Definition: ztrsm.f:180
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