[aspect-devel] muparser and Floating point exception from divide by zero.

[Magali Billen]

Thanks for you help with this. I can rewrite this using the lazy expression ( ? : ), nesting them does not seem to be a problem.

Also, good idea to add some examples with this in the cookbooks … I had seen the ? :  syntax on the muparser page, but noticed that it
was not in any of the examples for aspect, so I wasn’t sure if I could use it or not.
-Magali


> On Jun 30, 2018, at 6:43 PM, Bob Myhill <myhill.bob at gmail.com> wrote:
> 
> Mea culpa. Thanks for the info, Timo! 
> Bob
> 
> On Sat, 30 Jun 2018, 16:57 Timo Heister, <heister at clemson.edu <mailto:heister at clemson.edu>> wrote:
> Bob,
> 
> > You're using a muParser if syntax that was deprecated a few years ago.
> 
> This is not quite correct. "if(expression, A, B)" is actually an a
> function we register with function parser inside deal.II. The problem
> is of course that A and B are evaluated before the expression is
> checked and divisions by zero would generate an error. This never
> occurred to me before. Oops. :-)
> 
> > The new syntax uses lazy evaluation to evaluate only the required branch of the if-statement. Try this:
> >
> > x>0 ? TS+(TM-TS)*(1-erfc((YMAX-y)/(2*sqrt(K*x/VSUB)))) : TM
> 
> I checked and this does work (my example would be "(expression) ? (A)
> : (B)") . Great!
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