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LAPACK
3.7.0
LAPACK: Linear Algebra PACKage
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subroutine cgbtf2 | ( | integer | M, |
integer | N, | ||
integer | KL, | ||
integer | KU, | ||
complex, dimension( ldab, * ) | AB, | ||
integer | LDAB, | ||
integer, dimension( * ) | IPIV, | ||
integer | INFO | ||
) |
CGBTF2 computes the LU factorization of a general band matrix using the unblocked version of the algorithm.
Download CGBTF2 + dependencies [TGZ] [ZIP] [TXT]
CGBTF2 computes an LU factorization of a complex m-by-n band matrix A using partial pivoting with row interchanges. This is the unblocked version of the algorithm, calling Level 2 BLAS.
[in] | M | M is INTEGER The number of rows of the matrix A. M >= 0. |
[in] | N | N is INTEGER The number of columns of the matrix A. N >= 0. |
[in] | KL | KL is INTEGER The number of subdiagonals within the band of A. KL >= 0. |
[in] | KU | KU is INTEGER The number of superdiagonals within the band of A. KU >= 0. |
[in,out] | AB | AB is COMPLEX array, dimension (LDAB,N) On entry, the matrix A in band storage, in rows KL+1 to 2*KL+KU+1; rows 1 to KL of the array need not be set. The j-th column of A is stored in the j-th column of the array AB as follows: AB(kl+ku+1+i-j,j) = A(i,j) for max(1,j-ku)<=i<=min(m,j+kl) On exit, details of the factorization: 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. See below for further details. |
[in] | LDAB | LDAB is INTEGER The leading dimension of the array AB. LDAB >= 2*KL+KU+1. |
[out] | IPIV | IPIV is INTEGER array, dimension (min(M,N)) The pivot indices; for 1 <= i <= min(M,N), row i of the matrix was interchanged with row IPIV(i). |
[out] | INFO | INFO is 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. The factorization has been completed, but the factor U is exactly singular, and division by zero will occur if it is used to solve a system of equations. |
The band storage scheme is illustrated by the following example, when M = N = 6, KL = 2, KU = 1: On entry: On exit: * * * + + + * * * u14 u25 u36 * * + + + + * * u13 u24 u35 u46 * a12 a23 a34 a45 a56 * u12 u23 u34 u45 u56 a11 a22 a33 a44 a55 a66 u11 u22 u33 u44 u55 u66 a21 a32 a43 a54 a65 * m21 m32 m43 m54 m65 * a31 a42 a53 a64 * * m31 m42 m53 m64 * * Array elements marked * are not used by the routine; elements marked + need not be set on entry, but are required by the routine to store elements of U, because of fill-in resulting from the row interchanges.
Definition at line 147 of file cgbtf2.f.