Tomek -
Similar trouble as before, but now in detect.F90. Answer to the points you
raised follow below.
The problem in detect.F90 is:
line 129:
do i = 3, nzn5
if (scrch2(i-1)*scrch2(i+1) >= 0.e0) scrch3(i) = 0.e0
end do
in my case this flips the sign scrch2(i-1)*scrch2(i+1)=1.d-24 due to rounding
and produces quite significant differences in the solution, e.g. +-100 Pa
where the pressure in the problem ranges from 80000 Pa - 100000 Pa.
Additionally I noted:
line 113:
if (a(i+1) - a(i-1) == 0.e0) then
temporary = small * smalla
else
I highly doubt that this will be true in a lot of cases. Is there any
rational for such a criteria, i.e. is it only here to avoid a div_by_zero ?
> I am generally against using floor-values in the code as they are (1)
> problem-dependent, and (2) mask some real problems.
(2) I perfectly agree, this is exactly why I am following these up, wouldn't
waste days of my time if I would think, well it's just rounding error. From
my experience only 10% of "rounding errors" are rounding errors.
> 1.e-10 or 1.e+10 does not really mean much when taken out
> of context. Hardwiring -10/+10 and -2/+2, as you suggested, may not be
> the best solution. Tying those constant to epsiln may work better.
adding these though gives the uses some appreciation of specific trouble
makers and an easy way of ruling these out. In my case I would rather live
with a hardwired constant than a rounding error of 100.d-0 in the pressure...
epsilon unfortunately does not cover all rounding errors either, especially
if you have to set convergence criteria for iterative solutions where it may
not be necessary and or desirable to converge to machine precision.
Nevertheless, it is an excellent default for all hardwired constants.
Markus.
-- _______________________________________________________________Markus Gross AMIMechE BEng (Hons.) Mechanical Engineering
Heriot Watt University Edinburgh School of Engineering and Physical Sciences James Nasmyth Building Edinburgh EH14 4AS UK
Member of IMechE, SPIE, CSME and VDI _______________________________________________________________
further contact:
Phone : +44 (0) 131 451 4737
UNiX talk: talk markus@lasersim.mce.hw.ac.uk
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"Plans are a place to begin," Grove said. "They rarely deliver you to where you expect. Make your plans knowing you are going to throw them away."
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