Plotting histogram from the discrete user defined function

[kanhaiya-gupta]

Hi,

I am trying to plot a histogram from a user defined discrete function. My function is
x and y are uniform distribution between (0,1) and w = x + y

f(w) = w for 0<=w<=1
= 2-w for 1<=w<=2
= 0 for otherwise

When I try to implement I don’t get any plot. I cannot figure out where my mistake is. I have attached my macros.ex5n.C (581 Bytes)

Thank you.
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[couet]

There was many mistakes in your code. Here is the corrected version:

double myfunction(double *x, double *par) {
   TRandom3 * generator = new TRandom3();
   double x1 = generator->Uniform(0,1);
   double y1 = generator->Uniform(0,1);
   double w1 = x1 + y1;
   if (w1>=0.&& w1<=1.){
      return w1;
   } else if (w1>1.&& w1<=2.) {
      return (2.-w1);
   } else {
      return 0.;
   };
}

void ex5n() {
   auto c1 = new TCanvas("canvas","Example",200,10,600,400);
   auto f1 = new TF1("f1",myfunction,0,2,0);
   auto h1 = new TH1F("h1", "test", 100, 0., 2.);
   h1->FillRandom("f1",1000000);
   h1->Draw();
}

[kanhaiya-gupta]

Thanks a lot!

[kanhaiya-gupta]

Does it (h1->FillRandom(“f1”,1000000) command fill the random number inside the Histogram or fills the numbers defined by the function “myfunction”?

I want to fill the numbers according to myfunction. I don’t know if I am doing it correct.

[couet]

@kanhaiya-gupta

I want to fill the numbers according to myfunction. I don’t know if I am doing it correct.

Yes in principle it will generate 1000000 random points according to your function … Is that what you want ? @moneta can tell you more.

[moneta]

Yes it will generate 1000000 random points according to your function and use them to fill the histogram!

[kanhaiya-gupta]

Does it make sense to my code? Because I am generating the random numbers in myfunction. And than want to fill that w1 which is sum of x1 and y1?

But again I generate random numbers according to function? (h1->FillRandom(“f1”,1000000)

How can I fill the numbers generated by my function?

Thank you.

[couet]

The best is to Draw your function and see if that’s what you want. if you Draw it you will get the following flat distribution:

Is it what you are looking for ?

[kanhaiya-gupta]

I expect the graph shown in 2nd row (b). Does (h1->FillN(“f1”,1000000); ) will work? I don’t know how to implement it.

[couet]

The definition of your function is not correct i guess.

[kanhaiya-gupta]

The function is

I am trying to plot a histogram from a user defined discrete function. My function is
x and y are uniform distribution between (0,1) and w = x + y

f(w) = w for 0<=w<=1
= 2-w for 1<=w<=2
= 0 for otherwise

My confusion is if i implement the code using h1->FillRandom(“f1”,10000); I am doing it twice.

[couet]

// f(w) = w for 0<=w<=1
// = 2-w for 1<=w<=2
// = 0 for otherwise

double myfunction(double *w, double *par) {
   if (w[0] >= 0. && w[0] <= 1.){
      return w[0];
   } else if (w[0]>1. &&  w[0]<=2.) {
      return (2.-w[0]);
   } else {
      return 0.;
   };
}

void ex5n() {
   auto c1 = new TCanvas("canvas","Example",200,10,600,400);
   auto f1 = new TF1("f1",myfunction,0,2,0);
   auto h1 = new TH1F("h1", "test", 100, 0., 2.);
   h1->FillRandom("f1",1000000);
   h1->Draw();
}

[kanhaiya-gupta]

Thank you so much.