#include "blaswrap.h" #include "f2c.h" /* Subroutine */ int sgtsv_(integer *n, integer *nrhs, real *dl, real *d__, real *du, real *b, integer *ldb, integer *info) { /* -- LAPACK routine (version 3.1) -- Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. November 2006 Purpose ======= SGTSV 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) REAL 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) REAL 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) REAL 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) REAL 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. ===================================================================== Parameter adjustments */ /* System generated locals */ integer b_dim1, b_offset, i__1, i__2; real r__1, r__2; /* Local variables */ static integer i__, j; static real fact, temp; extern /* Subroutine */ int xerbla_(char *, integer *); --dl; --d__; --du; b_dim1 = *ldb; b_offset = 1 + b_dim1; b -= b_offset; /* Function Body */ *info = 0; if (*n < 0) { *info = -1; } else if (*nrhs < 0) { *info = -2; } else if (*ldb < max(1,*n)) { *info = -7; } if (*info != 0) { i__1 = -(*info); xerbla_("SGTSV ", &i__1); return 0; } if (*n == 0) { return 0; } if (*nrhs == 1) { i__1 = *n - 2; for (i__ = 1; i__ <= i__1; ++i__) { if ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2))) { /* No row interchange required */ if (d__[i__] != 0.f) { fact = dl[i__] / d__[i__]; d__[i__ + 1] -= fact * du[i__]; b[i__ + 1 + b_dim1] -= fact * b[i__ + b_dim1]; } else { *info = i__; return 0; } dl[i__] = 0.f; } else { /* Interchange rows I and I+1 */ fact = d__[i__] / dl[i__]; d__[i__] = dl[i__]; temp = d__[i__ + 1]; d__[i__ + 1] = du[i__] - fact * temp; dl[i__] = du[i__ + 1]; du[i__ + 1] = -fact * dl[i__]; du[i__] = temp; temp = b[i__ + b_dim1]; b[i__ + b_dim1] = b[i__ + 1 + b_dim1]; b[i__ + 1 + b_dim1] = temp - fact * b[i__ + 1 + b_dim1]; } /* L10: */ } if (*n > 1) { i__ = *n - 1; if ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2))) { if (d__[i__] != 0.f) { fact = dl[i__] / d__[i__]; d__[i__ + 1] -= fact * du[i__]; b[i__ + 1 + b_dim1] -= fact * b[i__ + b_dim1]; } else { *info = i__; return 0; } } else { fact = d__[i__] / dl[i__]; d__[i__] = dl[i__]; temp = d__[i__ + 1]; d__[i__ + 1] = du[i__] - fact * temp; du[i__] = temp; temp = b[i__ + b_dim1]; b[i__ + b_dim1] = b[i__ + 1 + b_dim1]; b[i__ + 1 + b_dim1] = temp - fact * b[i__ + 1 + b_dim1]; } } if (d__[*n] == 0.f) { *info = *n; return 0; } } else { i__1 = *n - 2; for (i__ = 1; i__ <= i__1; ++i__) { if ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2))) { /* No row interchange required */ if (d__[i__] != 0.f) { fact = dl[i__] / d__[i__]; d__[i__ + 1] -= fact * du[i__]; i__2 = *nrhs; for (j = 1; j <= i__2; ++j) { b[i__ + 1 + j * b_dim1] -= fact * b[i__ + j * b_dim1]; /* L20: */ } } else { *info = i__; return 0; } dl[i__] = 0.f; } else { /* Interchange rows I and I+1 */ fact = d__[i__] / dl[i__]; d__[i__] = dl[i__]; temp = d__[i__ + 1]; d__[i__ + 1] = du[i__] - fact * temp; dl[i__] = du[i__ + 1]; du[i__ + 1] = -fact * dl[i__]; du[i__] = temp; i__2 = *nrhs; for (j = 1; j <= i__2; ++j) { temp = b[i__ + j * b_dim1]; b[i__ + j * b_dim1] = b[i__ + 1 + j * b_dim1]; b[i__ + 1 + j * b_dim1] = temp - fact * b[i__ + 1 + j * b_dim1]; /* L30: */ } } /* L40: */ } if (*n > 1) { i__ = *n - 1; if ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2))) { if (d__[i__] != 0.f) { fact = dl[i__] / d__[i__]; d__[i__ + 1] -= fact * du[i__]; i__1 = *nrhs; for (j = 1; j <= i__1; ++j) { b[i__ + 1 + j * b_dim1] -= fact * b[i__ + j * b_dim1]; /* L50: */ } } else { *info = i__; return 0; } } else { fact = d__[i__] / dl[i__]; d__[i__] = dl[i__]; temp = d__[i__ + 1]; d__[i__ + 1] = du[i__] - fact * temp; du[i__] = temp; i__1 = *nrhs; for (j = 1; j <= i__1; ++j) { temp = b[i__ + j * b_dim1]; b[i__ + j * b_dim1] = b[i__ + 1 + j * b_dim1]; b[i__ + 1 + j * b_dim1] = temp - fact * b[i__ + 1 + j * b_dim1]; /* L60: */ } } } if (d__[*n] == 0.f) { *info = *n; return 0; } } /* Back solve with the matrix U from the factorization. */ if (*nrhs <= 2) { j = 1; L70: b[*n + j * b_dim1] /= d__[*n]; if (*n > 1) { b[*n - 1 + j * b_dim1] = (b[*n - 1 + j * b_dim1] - du[*n - 1] * b[ *n + j * b_dim1]) / d__[*n - 1]; } for (i__ = *n - 2; i__ >= 1; --i__) { b[i__ + j * b_dim1] = (b[i__ + j * b_dim1] - du[i__] * b[i__ + 1 + j * b_dim1] - dl[i__] * b[i__ + 2 + j * b_dim1]) / d__[ i__]; /* L80: */ } if (j < *nrhs) { ++j; goto L70; } } else { i__1 = *nrhs; for (j = 1; j <= i__1; ++j) { b[*n + j * b_dim1] /= d__[*n]; if (*n > 1) { b[*n - 1 + j * b_dim1] = (b[*n - 1 + j * b_dim1] - du[*n - 1] * b[*n + j * b_dim1]) / d__[*n - 1]; } for (i__ = *n - 2; i__ >= 1; --i__) { b[i__ + j * b_dim1] = (b[i__ + j * b_dim1] - du[i__] * b[i__ + 1 + j * b_dim1] - dl[i__] * b[i__ + 2 + j * b_dim1]) / d__[i__]; /* L90: */ } /* L100: */ } } return 0; /* End of SGTSV */ } /* sgtsv_ */