DTRCO - DTRCO estimates the condition of a double precision triangular
T DOUBLE PRECISION(LDT,N)
T contains the triangular matrix. The zero
elements of the matrix are not referenced, and
the corresponding elements of the array can be
used to store other information.
LDT is the leading dimension of the array T.
N is the order of the system.
= 0 T is lower triangular.
= nonzero T is upper triangular. On Return
RCOND DOUBLE PRECISION
an estimate of the reciprocal condition of T .
For the system T*X = B , relative perturbations
in T and B of size EPSILON may cause
relative perturbations in X of size EPSILON/RCOND .
If RCOND is so small that the logical expression
1.0 + RCOND .EQ. 1.0
is true, then T may be singular to working
precision. In particular, RCOND is zero if
exact singularity is detected or the estimate
Z DOUBLE PRECISION(N)
a work vector whose contents are usually unimportant.
If T is close to a singular matrix, then Z is
an approximate null vector in the sense that
NORM(A*Z) = RCOND*NORM(A)*NORM(Z) . LINPACK. This version dated
08/14/78 . Cleve Moler, University of New Mexico, Argonne National Lab.
Subroutines and Functions BLAS DAXPY,DSCAL,DASUM Fortran DABS,DMAX1,DSIGN
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