Re: problem with passing arrays in TF2.Draw()

Rene Brun (Rene.Brun@cern.ch)
Sun, 10 May 1998 17:33:01 +0200


Petar,
You have an error in your program. x[2] was never defined.
Remember addressing starts at 0 in C++.
See my comments in the code below.

Rene Brun

Petar Maksimovic wrote:
>
> Fellow rooters,
>
> I would appreciate if somebody could spare a minute and look over (and
> perhaps try running) the macro given below, in which I attempt to plot
> a trivial 2-D function (using TF2.Draw()). I'm using root 2.00/05,
> and the problem exists on both IRIX 6.2 and Linux RedHat 5.0.
>
> Thanks a lot!
>
> Petar
>
> // file: test.C
> //____________________________________________________________________________
> // tfun2() called from tfun1()
> //
> Double_t tfun2( Double_t *ee)
> {
> printf("ee[] = %f %f %f\n", ee[0], ee[1], ee[2]);
> return ee[0]+ee[1]+ee[2];
> }
>
> //____________________________________________________________________________
> // tfun1() is used in TF2 constructor and called by TF2.Draw()
> //
> Double_t tfun1(Double_t *x, Double_t *par)
> {
> Double_t res; // the result
> Double_t xe[3]; // the array we'll try to pass
>
> // put some values in xe[] (they are arbitrary)
> // xe[0] = x[1] + 0.845; //<====== these two lines are wrong
> // xe[1] = x[2] * x[1] * 0.246;
// replaced by
xe[0] = x[0] + 0.845;
xe[1] = x[1] * x[0] * 0.246;
> xe[2] = 0.941;
>
> printf("xe[] = %f %f %f\n", xe[0], xe[1], xe[2]);
>
> // call tfun2()
> res = tfun2(xe);
>
> printf("Result = %f\n", res);
> return res;
> }
>
> I load and execute the above functions with:
>
> root [0] .L test.C
> root [1] TF2 *f2 = new TF2("test",tfun1,0,1,0,1,0);
> root [2] f2->Draw()
>
> And get hundreds of the following error messages:
>
> Error: Array index out of range xe+2147351296 valid upto xe[2] FILE:/home/lv48/petar/root/./test.C LINE:10
> Error: Array index out of range xe+1072569516 valid upto xe[2] FILE:/home/lv48/petar/root/./test.C LINE:10
> Error: Array index out of range xe+57 valid upto xe[2] FILE:/home/lv48/petar/root/./test.C LINE:10
> xe[] = 0.941000 0.000000 0.941000
>
> The problem does not appear when I call tfun1() interactively,
> e.g. by creating x,par in root shell, and printing its value:
>
> root[77] printf("%f\n", tfun1(x,par));
>
> Am I overlooking something? Thanks for any ideas on where to look...