Possible TF1 Parsing bug?

ROOT
1

Can anyone explain what’s going on here?

pwaller@jupiter ~ $ root-config --version --svn-revision 5.19/01 21745 pwaller@jupiter ~ $ root -l root [0] TF1 f("f", "TMath::BreitWigner(x,0,1)", -10, 10); f.Draw() <TCanvas::MakeDefCanvas>: created default TCanvas with name c1
The above works exactly as expected, drawing a BW centred on 0.

Again, fine, centred about 5.

Gwuh? What on earth? It’s drawing it upside down with a width of 5. And it seems to ignore the third parameter.

An attempt to rectify:

Gives nothing. It turns out that this one ignores the third parameter and treats the second as the width.

The above works, drawing a BW centred on -1 with gamma = 1.

Is this a bug in ROOT, or am I doing something fundamentally wrong? I can provide plots if necessary.

Regards,

  • Peter

P.S. Some more strange behavior: If I set the Y log scale, then the Z log scale (it’s only a 1D plot, I know, but bare with me) – upon setting the LogZ, the Y scale changes. Is this another bug? Shouldn’t the Y scale be unaffected?

2

Use the form

TF1 f("f", "TMath::BreitWigner(x,[0],[1])", -10, 10); f.SetParameters(-5,1); f.Draw();
There is apparently a problem when giving your expression containing a negative sign. TMath::BreitWigner itself is correct.I will investigate once I will be back from my trip.

Rene

3 

How about this expression? It contains no negative signs?

How about this expression? It contains no negative signs?

4

Any updates on this?

5

Hi,

This problem has been fixed in the head of the SVN trunk.

Thanks for your patience.
Philippe.