🚀 go-pugleaf

iwelch@agsm.ucla.edu (Ivo Welch) writes:


*I  have  the 1989 version  of   Numerical Recipees  in  C, both   in book  and
*electronic form. I believe I have found a bug---or at least  a nuisance.  When
*a matrix  contains some  extreme values,  it   is  possible  to get  an access
*violation.

[ Code deleted. ]

*# note that l ends with a value of 0 if the loop exits. Typically,
*# rv1[l]=0, so the loop is exited early---no problem then. However,
*# if the matrix is poorly setup (and I have had such a case), rv1[1]
*# can become NaN (0/0), and the loop completes rather than breaks.
*# I believe rv1[1] turned into NaN, since my matrix contained an IEEE
*# -Inf.

I have had the same problem, but *only* when my input matrix contained
an Inf or NaN as appears to be the case in your example.  So, unless
you intend to work with infinities, it would appear that the code
works.  However, the fact that the program produces a segmentation
violation and core dumps as the result of a data error *is* annoying.

*# I presume this problem can be fixed if the condition reads l>=2,
*# and nm=l-1 is moved into both the start and iteration.

Perhaps you should just check for l == 0 at the end of the loop and
exit gracefully with an error message.  If you disallow l = 1 in the
body of the loop, the code may not work properly.  I think there is a
comment in the book (if not in the code) that rv1[1] is always zero so
that the loop will always exit before l = 0.  If rv1[1] is not zero,
there must be something wrong with the data.  Therefore, you could
check the value of rv1[1] to see if it is correct at various points in
the code.

Darrell

P.S. I would also be interested in seeing a bug list for Numerical
Recipes in C is anyone has it on line.