[ROOT] RE: Using a user defined function from the command line

From: Philippe Canal (pcanal@fnal.gov)
Date: Mon Jun 09 2003 - 17:10:52 MEST 

Hi Stelios,

Currently you can not use any user defined free-standing function in the
TTree::Draw command.  You can only use the function defined in TFormula and
the method of the objects stored in the tree.

In order to use a user defined free-standing function you currently have to
use and customize the result of MakeSelector.

We are currently working on improvements to TTree::Draw that will simplify
this type of usage.

Cheers,
Philippe.

-----Original Message-----
From: owner-about-root@listserv.fnal.gov
[mailto:owner-about-root@listserv.fnal.gov]On Behalf Of Stilianos Kesisoglou
Sent: Sunday, June 08, 2003 8:14 PM
To: roottalk@root.cern.ch; roottalk@pcroot.cern.ch; about-root@fnal.gov
Subject: Using a user defined function from the command line


Hi,

    Is it possible to use a user defined function from the command line on
ROOT
when drawing a histogram?

    For example I have the function:

#include <cmath>

float angl(float y, float phi)
{
    const float pi = 3.141592654;

    float angle;

    if (y==0.0) {
        angle = pi;
    } else if (y>0.0) {
        angle = phi;
    } else {
        angle = phi-2*pi;
    }

    return angle;

}

and I load it to ROOT:

root[] .L angl.C

    I can use it from the command line if I want to:

root[] angl(0.5,0.58)

with no problem, but what about when I plot a histogram?

root[] myTree->Draw("angl(y,phi)")

(where "y" and "phi" are variables of the tree "myTree")

    I try to do it and ROOT complains. I would like to do it exactly as
if that function was let's say "atan2"

    Any suggestions?

    Thanks!

Stelios.

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