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! DTBLOK gets the determinant of an almost block diagonal matrix.
Discussion:
The matrix's PLU factorization must have been obtained
previously by FCBLOK.
The logarithm of the determinant is computed instead of the
determinant itself to avoid the danger of overflow or underflow
inherent in this calculation.
Modified:
14 February 2007
Author:
Carl DeBoor
Reference:
Carl DeBoor,
A Practical Guide to Splines,
Springer, 2001,
ISBN: 0387953663,
LC: QA1.A647.v27.
Parameters:
Input, real ( kind = 8 ) BLOKS(*), the factorization of A computed
by FCBLOK.
Input, integer ( kind = 4 ) INTEGS(3,NBLOKS), describes the block
structure of A.
Input, integer ( kind = 4 ) NBLOKS, the number of blocks in A.
Input, integer ( kind = 4 ) IPIVOT(*), pivoting information.
The dimension of IPIVOT is the sum ( INTEGS(1,1:NBLOKS) ).
Input, integer ( kind = 4 ) IFLAG, = (-1)**(number of interchanges during
factorization) if successful, otherwise IFLAG = 0.
Output, real ( kind = 8 ) DETSGN, the sign of the determinant.
Output, real ( kind = 8 ) DETLOG, the natural logarithm of the
determinant, if the determinant is not zero. If the determinant
is 0, then DETLOG is returned as 0.
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| real(kind=8) | :: | bloks(*) | ||||
| integer(kind=4) | :: | integs(3,nbloks) | ||||
| integer(kind=4) | :: | nbloks | ||||
| integer(kind=4) | :: | ipivot(1) | ||||
| integer(kind=4) | :: | iflag | ||||
| real(kind=8) | :: | detsgn | ||||
| real(kind=8) | :: | detlog |