Re: dynamical versus non dynamical for TH1F

From: Marc Escalier <escalier_at_lal.in2p3.fr>
Date: Sat, 23 Jan 2010 22:40:35 +0100

thanks Andriy for the information

i still put the whole list because somebody could have important comments.

i would have some other questions to understand better, if you don't mind :

1. functionnality :
   > is that, according to C++ rules, the object myhisto will be destroyed after
   > exiting of scope, e.g. when your macro will terminate (if you draw this
   > histogram in macro, the plot will disappear from TCanvas).
   

suppose i have a program with something like ...
if (withToDoPlot1) {

    TCanvas *mycanvas=new TCanvas(...)
    TH1F *myhisto1=new TH1F(...)
    "fill of myhisto1"
    "draw of myhisto1"
}

and an another version, the same, but without pointer i mean
if (...) {

   TCanvas mycanvas(...)
   TH1F myhisto(...)
...
...draw()
}

==>what will be the difference ?

B) performances :
i just made a dummy test of using or not using dynamical allocation, the performance difference is huge : the dynamical is much more slower

example :
(in addition, in this example, i didn't do the "delete", which is "forbidden", just to save a bit more time : even with that, dynamical allocation is still very slow)

example :

1)the dynamic way :
0.309 second to run on a given computer
(i check that the differences of processing time is relevant with regards to fluctuations)

#include <iostream>

int main()
{

   class person
   {
   public :
     int age;
   };

   for (int j=0;j<1000;j++) {

     for (int i=0;i<100000;i++) {
       class person *marc=new person();
       marc->age=33;

       // std::cout << "age de marc=" << marc->age << std::endl;
     }

     //  delete person; (notice i don't delete to save time, but i don't 

have the "right"

   }
}

2)the static way (actually, i'm not sure that "static" is the good word :
on the same computer :
6.3 second : much more slower !!!

#include <iostream>

int main()
{

   class person
   {
   public :
     int age;
   };

   for (int j=0;j<1000;j++) {

     for (int i=0;i<100000;i++) {
       class person *marc=new person();
       marc->age=33;

       // std::cout << "age de marc=" << marc->age << std::endl;
     }

     //  delete person;

   }
}

regards

---

On Sat, 23 Jan 2010, Andriy Zatserklyaniy wrote:

> Hi Mark,

>

> In short: a recommended way is to create you histogram in heap

>

> TH1F *myhisto=new TH1F(...)

>

> Otherwise you have to specify what do you want to optimise: speed, memory
> usage, etc.

>

> Well known drawback of

>

> TH1F myhisto(...)

>

> is that, according to C++ rules, the object myhisto will be destroyed after
> exiting of scope, e.g. when your macro will terminate (if you draw this
> histogram in macro, the plot will disappear from TCanvas).

>

> Cheers,
> Andrei.

>

> On Sat, Jan 23, 2010 at 10:48 AM, Marc Escalier <escalier_at_lal.in2p3.fr>wrote:

>
>> Hello,
>>
>> i'm using a basic root program (.C) that allows to make some histograms of
>> variables of a given ntuple (a .root file)
>>
>> Up to now, i created the histogram dynamically with
>> TH1F *myhisto=new TH1F(...)
>>
>> i was wondering what it the more optimal (in terms of memory, cpu usage, or
>> any other criterious you know better than me) way to do ? :
>>
>> *this kind of dynamical allocation
>>
>> or
>>
>> *a non dynamical allocation
>> (i mean :
>> TH1F myhisto(...)
>> )
>>
>> (just in case : i do always the same plots and there variables are always
>> in the ntuple)
>>
>> thanks !
>>
>> (i'll reply in private to answers to prevent spamming you all)
>>
>>
>

Received on Sat Jan 23 2010 - 22:40:40 CET