Re: check inside a loop?

*To*: mathgroup at smc.vnet.net*Subject*: [mg80828] Re: [mg80736] check inside a loop?*From*: bsyehuda at gmail.com*Date*: Mon, 3 Sep 2007 06:15:39 -0400 (EDT)*References*: <200708310341.XAA07769@smc.twtelecom.net>

Hi, For the specific example you posted, first using f[x_]= rather then f[x_]:= forces Mathematica to evaluate the right hand side of the definition at the time of definition of f, and it is replaced by Csc[x] which does not return an error message. It returns ComplexInfinity without the message. In addition, use Pi with capital P Next, For and Do loops DO NOT return values. you need to use some sort of breaking mechanism or collect the values of i when the error is generated, for example, Catch and Throw (breaks at the first error) or Reap and Sow (collect all errors) Reap[Do[If[Check[f[i], "zzz"] == "zzz", Sow[i]], {i, 0, 2, 1/4}]] // Rest or Catch[Do[If[Check[f[i], "zzz"] == "zzz", Throw[i]], {i, 0, 2, 1/4}]] yehuda On 8/31/07, Jeremy Price < cfgauss at u.washington.edu> wrote: > > I have a large loop that is ndsolving/nintegrating a bunch of things, and > a > lot of the results give me various errors due to the equations not being > very nice. I'd like to have a way to check what values of my paramaters > are > causing the errors, but I can't find a way to do that inside a loop. > > For example, if I have something like, > f[x_] = 1/Sin[2 pi x] > > For[ i=1, i < 1000, i++, > f[i] > ] > > I'm going to get a lot of "Power::infy: Infinite expression 1/0 > encountered." errors. I'd like to see what values of i these occur at. > > I've tried something like > > For[ i=1, i<1000, i++, > Check[ f[i] , i] > ] > > But this just returns "Power::infy: Infinite expression 1/0 encountered." > errors without the i vaule, which is different than I get by evaluating > something like > Check[ f[0],0] > Which returns: > Power::infy: Infinite expression 1/0 encountered. > 0 > > Is there any way I can get it to return the index that the error occured > at > for every error that occurs inside of the loop? > > >