Log scale TH2D

ROOT
1

Hi,

I have a TH2D whose y-axis shows the base 10 logarithm of a certain physical quantity; thus, the y-axis values are -3, -2,…,1,2; I simply want to turn these numbers into 0.001, 0.02,…,10, 100, respectively. However, I do not want this modification to affect the plot: I already have a log-scale, I only want to modify the y-axis values.

How could I do?

Thank you!

2

Hi,
try the att. macro
Otto
logaxis.C (523 Bytes)

3

I guess you can try:

h2->GetYaxis()->SetLimits(0.001,100);

4

It does not work.

However, this is my macro:

#include "TCanvas.h"
#include "TStyle.h"
#include "TH2.h"
#include <fstream>
#include "TLatex.h"
#include "TAttLine.h"
#include "TGraph.h"

void mymacro() {

	TCanvas *mymacro = new TCanvas("plot","plot", 1100, 1100);
	
	TH2D *r1 = new TH2D("g1","g1", 100, 150, 1000, 100, -14, 6);

	gStyle->SetOptStat(0);
	gStyle->SetOptTitle(0);

	ifstream red1 ("path/RED");

	double x_bin;
	double y_bin;
	double ylog;
	int i=0;

	while(red1>>x_bin>>y_bin){
		r1->Fill(x_bin, y_bin);
		i++;
		}

	r1->SetFillColor(kRed);

	gStyle->SetPalette(1);
	
	r1->Draw("box");

	r1->GetYaxis()->SetRangeUser(-11,4);

	gPad->RedrawAxis();

	mymacro->Print("myMacro.pdf");

}

#ifndef __CINT__
int main() {
mymacro();
return 0 ; }
#endif

The RED file can be found here: dropbox.com/s/ohd7jos6mpe65z5/RED?dl=0.

As you can see, the origial y-axis range is (-14,6); then, I restrict it to (-11,4).

5

I tried it; this is the result: dropbox.com/s/7kmd7g9flli88 … o.pdf?dl=0

This is the macro that produced it:


#include "TCanvas.h"
#include "TStyle.h"
#include "TH2.h"
#include <fstream>
#include "TLatex.h"
#include "TAttLine.h"
#include "TGraph.h"
#include "TGaxis.h"
#include "TMath.h"

void mymacro() {

	TCanvas *mymacro = new TCanvas("plot","plot", 1100, 1100);

	TH2D *r1 = new TH2D("r1","y-axis title", 100, 150, 1000, 100, -14, 6);

	gStyle->SetOptStat(0);

	ifstream red1 ("/home/d/Scrivania/myMacro/log10_ggF_A_hZ_tautaull_TH_vs_mA_RED");

	double x_bin;
	double y_bin;
	double ylog;
	int i=0;

	while(red1>>x_bin>>y_bin){
		r1->Fill(x_bin, y_bin);
		i++;
		}

	r1->SetFillColor(kRed);       

	r1->Draw("box");

	TGaxis *nya = new TGaxis(150, -14, 150, 6,  TMath::Power(10,-14), TMath::Power(10,6), 510, "G");
	r1->GetYaxis()->SetLabelOffset(-100);
	nya->Draw();

	r1->GetXaxis()->SetTitle("x-axis title");

	mymacro->Print("myMacro.pdf");

}

#ifndef __CINT__
int main() {
mymacro();
return 0 ; }
#endif

However, I do not know where those intermediate small black marks on the y-axis come from; I do not know what they mean. How could I delete them?

6 
void mymacro1() {

   TCanvas *mymacro = new TCanvas("plot","plot", 1100, 1100);

   TH2D *r1 = new TH2D("g1","g1", 100, 150, 1000, 100, 0.001, 100.);

   gStyle->SetOptStat(0);
   gStyle->SetOptTitle(0);

   ifstream red1 ("RED.txt");

   double x_bin;
   double y_bin;
   double y_bin2;

   double ylog;
   int i=0;

   while(red1>>x_bin>>y_bin){
      y_bin2 = ((y_bin+14)/20)*(100-0.001)+0.001;
      r1->Fill(x_bin, y_bin2);
      i++;
   }
   r1->SetFillColor(kRed);
   r1->Draw("box");
}
7

If y_bin were equal to 0 y_bin2 should be equal to 1; however, this does not happen by using your code. Moreover, the y-axis I obtain is not the right one.

The result I previously obtained (dropbox.com/s/7kmd7g9flli88 … o.pdf?dl=0) was fine except for those strange marks on the y-axis.

8

Hi

“those strange marks on the y-axis” are the secondary tickmarks.
Its very hard (question to Olivier: impossible???) to get rid off.
In principle setting ndiv (normally 510) = 10 should do it,
but log scales seem tricky.

Otto

9

That’s right, the secondary ticks can not be removed in log scale.

10

It does not work.

Are there any other methods to modify the y-axis?

11

Hi,
the following should do the trick:

void logaxis()
{
	TCanvas *c = new TCanvas("c1", "c1", 10, 10, 400, 800);
	Double_t fromy = -14, toy = 6;
	TH2D* h2 = new TH2D("h2", "h2", 50,0,50, 50, fromy, toy);
	h2->Draw();
	Double_t x1 = h2->GetXaxis()->GetXmin();
	Double_t y1 = h2->GetYaxis()->GetXmin();
	Double_t y2 = h2->GetYaxis()->GetXmax();
	h2->GetYaxis()->SetNdivisions(20);	// make sure no 2nd ticks
	TGaxis *nya = new TGaxis(x1, y1, x1, y2,  
		TMath::Power(10,fromy), TMath::Power(10,toy), 20, "SG");
	h2->GetYaxis()->SetLabelOffset(-100); // hide orig labels
	nya->SetTickLength(0);		// hide ticks, see option "S" above
	nya->Draw();
}

Caveat: This only works with integer limits when ticks of the linear and log
scale coincide

Otto