# Ubuntu Feisty 7.04 manual page repository

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### NAME

ZGBTRS - solve a system of linear equations A * X = B, A**T * X = B, or A**H * X = B with a general band matrix A using the LU factorization computed by ZGBTRF

### SYNOPSIS

SUBROUTINE ZGBTRS( TRANS, N, KL, KU, NRHS, AB, LDAB, IPIV, B, LDB, INFO ) CHARACTER TRANS INTEGER INFO, KL, KU, LDAB, LDB, N, NRHS INTEGER IPIV( * ) COMPLEX*16 AB( LDAB, * ), B( LDB, * )

### PURPOSE

ZGBTRS solves a system of linear equations A * X = B, A**T * X = B, or A**H * X = B with a general band matrix A using the LU factorization computed by ZGBTRF.

### ARGUMENTS

TRANS (input) 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) N (input) INTEGER The order of the matrix A. N >= 0. KL (input) INTEGER The number of subdiagonals within the band of A. KL >= 0. KU (input) INTEGER The number of superdiagonals within the band of A. KU >= 0. NRHS (input) INTEGER The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0. AB (input) COMPLEX*16 array, dimension (LDAB,N) Details of the LU factorization of the band matrix A, as com‐ puted by ZGBTRF. U is stored as an upper triangular band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and the multipliers used during the factorization are stored in rows KL+KU+2 to 2*KL+KU+1. LDAB (input) INTEGER The leading dimension of the array AB. LDAB >= 2*KL+KU+1. IPIV (input) INTEGER array, dimension (N) The pivot indices; for 1 <= i <= N, row i of the matrix was interchanged with row IPIV(i). B (input/output) COMPLEX*16 array, dimension (LDB,NRHS) On entry, the right hand side matrix B. On exit, the 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