LAPACK  3.6.1
LAPACK: Linear Algebra PACKage
subroutine sptsv ( integer  N,
integer  NRHS,
real, dimension( * )  D,
real, dimension( * )  E,
real, dimension( ldb, * )  B,
integer  LDB,
integer  INFO 
)

SPTSV computes the solution to system of linear equations A * X = B for PT matrices

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Purpose: 
 SPTSV computes the solution to a real system of linear equations
 A*X = B, where A is an N-by-N symmetric positive definite tridiagonal
 matrix, and X and B are N-by-NRHS matrices.

 A is factored as A = L*D*L**T, and the factored form of A is then
 used to solve the system of equations.
Parameters
[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,out]D
          D is REAL array, dimension (N)
          On entry, the n diagonal elements of the tridiagonal matrix
          A.  On exit, the n diagonal elements of the diagonal matrix
          D from the factorization A = L*D*L**T.
[in,out]E
          E is REAL array, dimension (N-1)
          On entry, the (n-1) subdiagonal elements of the tridiagonal
          matrix A.  On exit, the (n-1) subdiagonal elements of the
          unit bidiagonal factor L from the L*D*L**T factorization of
          A.  (E can also be regarded as the superdiagonal of the unit
          bidiagonal factor U from the U**T*D*U factorization of A.)
[in,out]B
          B is REAL array, dimension (LDB,NRHS)
          On entry, the N-by-NRHS right hand side matrix B.
          On exit, if INFO = 0, the N-by-NRHS 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 leading minor of order i is not
                positive definite, and the solution has not been
                computed.  The factorization has not been completed
                unless i = N.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
September 2012

Definition at line 116 of file sptsv.f.

116 *
117 * -- LAPACK driver routine (version 3.4.2) --
118 * -- LAPACK is a software package provided by Univ. of Tennessee, --
119 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
120 * September 2012
121 *
122 * .. Scalar Arguments ..
123  INTEGER info, ldb, n, nrhs
124 * ..
125 * .. Array Arguments ..
126  REAL b( ldb, * ), d( * ), e( * )
127 * ..
128 *
129 * =====================================================================
130 *
131 * .. External Subroutines ..
132  EXTERNAL spttrf, spttrs, xerbla
133 * ..
134 * .. Intrinsic Functions ..
135  INTRINSIC max
136 * ..
137 * .. Executable Statements ..
138 *
139 * Test the input parameters.
140 *
141  info = 0
142  IF( n.LT.0 ) THEN
143  info = -1
144  ELSE IF( nrhs.LT.0 ) THEN
145  info = -2
146  ELSE IF( ldb.LT.max( 1, n ) ) THEN
147  info = -6
148  END IF
149  IF( info.NE.0 ) THEN
150  CALL xerbla( 'SPTSV ', -info )
151  RETURN
152  END IF
153 *
154 * Compute the L*D*L**T (or U**T*D*U) factorization of A.
155 *
156  CALL spttrf( n, d, e, info )
157  IF( info.EQ.0 ) THEN
158 *
159 * Solve the system A*X = B, overwriting B with X.
160 *
161  CALL spttrs( n, nrhs, d, e, b, ldb, info )
162  END IF
163  RETURN
164 *
165 * End of SPTSV
166 *
spttrf
subroutine spttrf(N, D, E, INFO)
SPTTRF
Definition: spttrf.f:93
xerbla
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
spttrs
subroutine spttrs(N, NRHS, D, E, B, LDB, INFO)
SPTTRS
Definition: spttrs.f:111

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