LAPACK 3.12.0 LAPACK: Linear Algebra PACKage
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◆ zpptrs()

 subroutine zpptrs ( character uplo, integer n, integer nrhs, complex*16, dimension( * ) ap, complex*16, dimension( ldb, * ) b, integer ldb, integer info )

ZPPTRS

Purpose:
``` ZPPTRS 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 ZPPTRF.```
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*16 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*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 107 of file zpptrs.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*16 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 xerbla, ztpsv
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( 'ZPPTRS', -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 ztpsv( '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 ztpsv( '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 ztpsv( '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 ztpsv( '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 ZPPTRS
199*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
subroutine ztpsv(uplo, trans, diag, n, ap, x, incx)
ZTPSV
Definition ztpsv.f:144
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