dgefa Subroutine

public subroutine dgefa(A, Lda, N, Ipvt, Info)

dgefa(3f) - [M_odepack::matrix] Factor a matrix using Gaussian elimination.

  subroutine dgefa(A,Lda,N,Ipvt,Info)
  real(kind=dp),intent(inout) :: A(Lda,*)
  integer,intent(in)          :: Lda
  integer,intent(in)          :: N
  integer,intent(out)         :: Ipvt(*)
  integer,intent(out)         :: Info

DESCRIPTION

DGEFA factors a double precision matrix by Gaussian elimination.

DGEFA is usually called by DGECO, but it can be called directly with a saving in time if RCOND is not needed. (Time for DGECO) = (1 + 9/N)*(Time for DGEFA) .

OPTIONS

A

the matrix to be factored.

LDA

the leading dimension of the array A .

N

the order of the matrix A .

RETURNS

A

an upper triangular matrix and the multipliers which were used to obtain it. The factorization can be written A = L*U where

L

is a product of permutation and unit lower triangular matrices and U is upper triangular.

IPVT

an integer vector of pivot indices.

INFO

: = 0 normal value. = K if U(K,K) .EQ. 0.0 . This is not an error condition for this subroutine, but it does indicate that DGESL or DGEDI will divide by zero if called. Use RCOND in DGECO for a reliable indication of singularity.

REFERENCES

J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W. Stewart, LINPACK Users’ Guide, SIAM, 1979.

Arguments