LAPACK 3.12.0 LAPACK: Linear Algebra PACKage
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## ◆ dpotrs()

 subroutine dpotrs ( character uplo, integer n, integer nrhs, double precision, dimension( lda, * ) a, integer lda, double precision, dimension( ldb, * ) b, integer ldb, integer info )

DPOTRS

Purpose:
``` DPOTRS solves a system of linear equations A*X = B with a symmetric
positive definite matrix A using the Cholesky factorization
A = U**T*U or A = L*L**T computed by DPOTRF.```
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 DOUBLE PRECISION array, dimension (LDA,N) The triangular factor U or L from the Cholesky factorization A = U**T*U or A = L*L**T, as computed by DPOTRF.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).``` [in,out] B ``` B is DOUBLE PRECISION 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 dpotrs.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 DOUBLE PRECISION A( LDA, * ), B( LDB, * )
121* ..
122*
123* =====================================================================
124*
125* .. Parameters ..
126 DOUBLE PRECISION ONE
127 parameter( one = 1.0d+0 )
128* ..
129* .. Local Scalars ..
130 LOGICAL UPPER
131* ..
132* .. External Functions ..
133 LOGICAL LSAME
134 EXTERNAL lsame
135* ..
136* .. External Subroutines ..
137 EXTERNAL dtrsm, xerbla
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( 'DPOTRS', -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**T *U.
172*
173* Solve U**T *X = B, overwriting B with X.
174*
175 CALL dtrsm( 'Left', 'Upper', 'Transpose', 'Non-unit', n, nrhs,
176 \$ one, a, lda, b, ldb )
177*
178* Solve U*X = B, overwriting B with X.
179*
180 CALL dtrsm( '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**T.
185*
186* Solve L*X = B, overwriting B with X.
187*
188 CALL dtrsm( 'Left', 'Lower', 'No transpose', 'Non-unit', n,
189 \$ nrhs, one, a, lda, b, ldb )
190*
191* Solve L**T *X = B, overwriting B with X.
192*
193 CALL dtrsm( 'Left', 'Lower', 'Transpose', 'Non-unit', n, nrhs,
194 \$ one, a, lda, b, ldb )
195 END IF
196*
197 RETURN
198*
199* End of DPOTRS
200*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
subroutine dtrsm(side, uplo, transa, diag, m, n, alpha, a, lda, b, ldb)
DTRSM
Definition dtrsm.f:181
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