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zgbtf2.f(3) LAPACK zgbtf2.f(3)

zgbtf2.f -

subroutine zgbtf2 (M, N, KL, KU, AB, LDAB, IPIV, INFO)
ZGBTF2 computes the LU factorization of a general band matrix using the unblocked version of the algorithm.

ZGBTF2 computes the LU factorization of a general band matrix using the unblocked version of the algorithm.
 ZGBTF2 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.
          M is INTEGER
          The number of rows of the matrix A.  M >= 0.
          N is INTEGER
          The number of columns of the matrix A.  N >= 0.
          KL is INTEGER
          The number of subdiagonals within the band of A.  KL >= 0.
          KU is INTEGER
          The number of superdiagonals within the band of A.  KU >= 0.
          AB is COMPLEX*16 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.
          LDAB is INTEGER
          The leading dimension of the array AB.  LDAB >= 2*KL+KU+1.
          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).
          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.
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
September 2012
Further Details:
  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 146 of file zgbtf2.f.

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