LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
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◆ ztptrs()

 subroutine ztptrs ( character UPLO, character TRANS, character DIAG, integer N, integer NRHS, complex*16, dimension( * ) AP, complex*16, dimension( ldb, * ) B, integer LDB, integer INFO )

ZTPTRS

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Purpose:
``` ZTPTRS solves a triangular system of the form

A * X = B,  A**T * X = B,  or  A**H * X = B,

where A is a triangular matrix of order N stored in packed format,
and B is an N-by-NRHS matrix.  A check is made to verify that A is
nonsingular.```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 = 'U': A is upper triangular; = 'L': A is lower triangular.``` [in] TRANS ``` TRANS is CHARACTER*1 Specifies the form of the system of equations: = 'N': A * X = B (No transpose) = 'T': A**T * X = B (Transpose) = 'C': A**H * X = B (Conjugate transpose)``` [in] DIAG ``` DIAG is CHARACTER*1 = 'N': A is non-unit triangular; = 'U': A is unit triangular.``` [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 upper or lower triangular matrix A, packed columnwise in a linear array. The j-th column of A is stored in the array AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(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, if INFO = 0, 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 > 0: if INFO = i, the i-th diagonal element of A is zero, indicating that the matrix is singular and the solutions X have not been computed.```

Definition at line 129 of file ztptrs.f.

130*
131* -- LAPACK computational routine --
132* -- LAPACK is a software package provided by Univ. of Tennessee, --
133* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
134*
135* .. Scalar Arguments ..
136 CHARACTER DIAG, TRANS, UPLO
137 INTEGER INFO, LDB, N, NRHS
138* ..
139* .. Array Arguments ..
140 COMPLEX*16 AP( * ), B( LDB, * )
141* ..
142*
143* =====================================================================
144*
145* .. Parameters ..
146 COMPLEX*16 ZERO
147 parameter( zero = ( 0.0d+0, 0.0d+0 ) )
148* ..
149* .. Local Scalars ..
150 LOGICAL NOUNIT, UPPER
151 INTEGER J, JC
152* ..
153* .. External Functions ..
154 LOGICAL LSAME
155 EXTERNAL lsame
156* ..
157* .. External Subroutines ..
158 EXTERNAL xerbla, ztpsv
159* ..
160* .. Intrinsic Functions ..
161 INTRINSIC max
162* ..
163* .. Executable Statements ..
164*
165* Test the input parameters.
166*
167 info = 0
168 upper = lsame( uplo, 'U' )
169 nounit = lsame( diag, 'N' )
170 IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
171 info = -1
172 ELSE IF( .NOT.lsame( trans, 'N' ) .AND. .NOT.
173 \$ lsame( trans, 'T' ) .AND. .NOT.lsame( trans, 'C' ) ) THEN
174 info = -2
175 ELSE IF( .NOT.nounit .AND. .NOT.lsame( diag, 'U' ) ) THEN
176 info = -3
177 ELSE IF( n.LT.0 ) THEN
178 info = -4
179 ELSE IF( nrhs.LT.0 ) THEN
180 info = -5
181 ELSE IF( ldb.LT.max( 1, n ) ) THEN
182 info = -8
183 END IF
184 IF( info.NE.0 ) THEN
185 CALL xerbla( 'ZTPTRS', -info )
186 RETURN
187 END IF
188*
189* Quick return if possible
190*
191 IF( n.EQ.0 )
192 \$ RETURN
193*
194* Check for singularity.
195*
196 IF( nounit ) THEN
197 IF( upper ) THEN
198 jc = 1
199 DO 10 info = 1, n
200 IF( ap( jc+info-1 ).EQ.zero )
201 \$ RETURN
202 jc = jc + info
203 10 CONTINUE
204 ELSE
205 jc = 1
206 DO 20 info = 1, n
207 IF( ap( jc ).EQ.zero )
208 \$ RETURN
209 jc = jc + n - info + 1
210 20 CONTINUE
211 END IF
212 END IF
213 info = 0
214*
215* Solve A * x = b, A**T * x = b, or A**H * x = b.
216*
217 DO 30 j = 1, nrhs
218 CALL ztpsv( uplo, trans, diag, n, ap, b( 1, j ), 1 )
219 30 CONTINUE
220*
221 RETURN
222*
223* End of ZTPTRS
224*
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine ztpsv(UPLO, TRANS, DIAG, N, AP, X, INCX)
ZTPSV
Definition: ztpsv.f:144
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