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dgtsv.f

      SUBROUTINE DGTSV( N, NRHS, DL, D, DU, B, LDB, INFO )
*
*  -- LAPACK routine (version 3.0) --
*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
*     Courant Institute, Argonne National Lab, and Rice University
*     October 31, 1999
*
*     .. Scalar Arguments ..
      INTEGER            INFO, LDB, N, NRHS
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   B( LDB, * ), D( * ), DL( * ), DU( * )
*     ..
*
*  Purpose
*  =======
*
*  DGTSV  solves the equation
*
*     A*X = B,
*
*  where A is an n by n tridiagonal matrix, by Gaussian elimination with
*  partial pivoting.
*
*  Note that the equation  A









































































'*X = B  may be solved by interchanging the*  order of the arguments DU and DL.**  Arguments*  =========**  N       (input) INTEGER*          The order of the matrix A.  N >= 0.**  NRHS    (input) INTEGER*          The number of right hand sides, i.e., the number of columns*          of the matrix B.  NRHS >= 0.**  DL      (input/output) DOUBLE PRECISION array, dimension (N-1)*          On entry, DL must contain the (n-1) sub-diagonal elements of*          A.**          On exit, DL is overwritten by the (n-2) elements of the*          second super-diagonal of the upper triangular matrix U from*          the LU factorization of A, in DL(1), ..., DL(n-2).**  D       (input/output) DOUBLE PRECISION array, dimension (N)*          On entry, D must contain the diagonal elements of A.**          On exit, D is overwritten by the n diagonal elements of U.**  DU      (input/output) DOUBLE PRECISION array, dimension (N-1)*          On entry, DU must contain the (n-1) super-diagonal elements*          of A.**          On exit, DU is overwritten by the (n-1) elements of the first*          super-diagonal of U.**  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)*          On entry, the N by NRHS matrix of right hand side matrix B.*          On exit, if INFO = 0, the N by NRHS solution matrix X.**  LDB     (input) INTEGER*          The leading dimension of the array B.  LDB >= max(1,N).**  INFO    (output) INTEGER*          = 0: successful exit*          < 0: if INFO = -i, the i-th argument had an illegal value*          > 0: if INFO = i, U(i,i) is exactly zero, and the solution*               has not been computed.  The factorization has not been*               completed unless i = N.**  =====================================================================**     .. Parameters ..      DOUBLE PRECISION   ZERO      PARAMETER          ( ZERO = 0.0D+0 )*     ..*     .. Local Scalars ..      INTEGER            I, J      DOUBLE PRECISION   FACT, TEMP*     ..*     .. Intrinsic Functions ..      INTRINSIC          ABS, MAX*     ..*     .. External Subroutines ..      EXTERNAL           XERBLA*     ..*     .. Executable Statements ..*      INFO = 0      IF( N.LT.0 ) THEN         INFO = -1      ELSE IF( NRHS.LT.0 ) THEN         INFO = -2      ELSE IF( LDB.LT.MAX( 1, N ) ) THEN         INFO = -7      END IF      IF( INFO.NE.0 ) THEN         CALL XERBLA( 'DGTSV 





































































































































































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