Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?gbtf2
Computes the LU factorization of a general band matrix using the unblocked version of the algorithm.
Syntax
call sgbtf2(m, n, kl, ku, ab, ldab, ipiv, info)
call dgbtf2(m, n, kl, ku, ab, ldab, ipiv, info)
call cgbtf2(m, n, kl, ku, ab, ldab, ipiv, info)
call zgbtf2(m, n, kl, ku, ab, ldab, ipiv, info)
Include Files
mkl.fi
Description
The routine forms the LU factorization of a general real/complex m -by- n band matrix A with kl sub-diagonals and ku super-diagonals. The routine uses partial pivoting with row interchanges and implements the unblocked version of the algorithm, calling Level 2 BLAS. See also ?gbtrf (Computes the LU factorization of a general m-by-n band matrix.) .
Input Parameters
- m
-
INTEGER. The number of rows in the matrix A. The value of m must be at least zero.
- n
-
INTEGER . The number of columns in A ( n≥ 0 ).
- kl
-
INTEGER . The number of sub-diagonals within the band of A ( kl≥ 0 ).
- ku
-
INTEGER . The number of super-diagonals within the band of A ( ku≥ 0 ).
- ab
-
REAL for sgbtf2 DOUBLE PRECISION for dgbtf2 COMPLEX for cgbtf2 DOUBLE COMPLEX for zgbtf2 . Array, DIMENSION ( ldab ,*). The array ab contains the matrix A in band storage (see Matrix Arguments ). The second dimension of ab must be at least max(1, n) .
- ldab
-
INTEGER . The leading dimension of the array ab . (ldab≥ 2kl + ku +1)
Output Parameters
- ab
-
Overwritten by details of the factorization. The diagonal and kl + ku super-diagonals of U are stored in the first 1 + kl + ku rows of ab . The multipliers used during the factorization are stored in the next kl rows.
- ipiv
-
INTEGER . Array, DIMENSION at least max(1,min( m , n )). The pivot indices: row i was interchanged with row ipiv(i).
info
INTEGER .
If info =0 , the execution is successful.
If info = -i , the i -th parameter had an illegal value.
If info = i , uii is 0. The factorization has been completed, but U is exactly singular. Division by 0 will occur if you use the factor U for solving a system of linear equations.