Cannot set log scale

Hi,

I have a macro to read some 1D histograms from a file and draw them. If I do gPad->SetLogy() before drawing, the histograms are nicely plotted in the log scale. However if I draw the histograms first and then try to switch to log scale (either by issuing gPad->SetLogy() or simply by right clicking the TPad and choosing log scale in the menu), I get the error:

Error in <THistPainter::PaintInit>: log scale requested with zero or negative argument (0.000000)

To overcome this problem I implemented a function (attached below) to loop through all the 1D histos on the gPad and SetMinimum() for all of them before calling gPad->SetLogy().

While this solves my problem, I still find it unintuitive to go through all this. While protection against negative arguments makes sense, bins with zero content are encountered quite often, so I am not sure if the current behavior is really desired for them.

My question: 1-Is there a gStyle kind of switch which turns off this error? (I am using ROOT 5.18/00.) 2-If not, could it be implemented in a future release of ROOT?

Thanks,

Erkcan

void PadToLogScale() {

   if ( gROOT->GetListOfCanvases()->GetEntries() == 0 ) return;    if ( gPad->GetLogy() ) return;

   TPad *oldpad = gPad;

   // Now loop through histos and find the extrema    TList *glist = oldpad->GetListOfPrimitives();    for (int i=0; i<glist->GetEntries(); ++i) {

     TObject *obj = glist->At(i);
     if ( obj->InheritsFrom("TH1") ) {

       // If there is a 2D histogram, don't do anything.
       if ( obj->InheritsFrom("TH2") ) return;

       TH1 *histo = (TH1*)obj;
       histo->SetMinimum();

     }

   gPad->SetLogy();
   gPad->Modified();

}

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V. Erkcan Ozcan
Research Fellow
University College London
Dept. of Physics & Astronomy