[ROOT] TGaxis

From: Mike Miller (miller@star.physics.yale.edu)
Date: Tue Jun 05 2001 - 00:47:20 MEST


Hello all, I'm trying do the following:

I have a 1-d histogram that I draw.  I then want to add some additional
x-axes that are non-linear.  So, I thought that I could use TGaxis and
specify a mapping function (TF1) to do so.  However, the result I get is
crazy, so I must not understand the meanings of the parameters passed to
the constructor, but the documentation points to TGaxis::PaintAxis and
that doesn't help very much.

Can you tell me:

1) If xmin, xmax, ymin, ymax specify the endopoints in global coordinates,
what does that really mean?  If I draw a canvas and then draw a histogram
on top of it, is the global x,y defined by the axes of the histogram?

2) What is ndiv really?  I thought that if it is really the number of
divisions, then ndiv=300 should give 300 divisions, but this doesn't seem
to be the case.

3) What is the relationship of the mapping that the TF1 should
establish.  If I have a function F(x) where x is the independent variable
of my original Histogram, and F(x) has a given range Fmin and Fmax, how do
I translate this into what TGaxis expects?

4) Why does TGaxis have a constructor that takes the char* name of a
function instead of a pointer to a TF1?  Seems like this is dangerous and
easy to change...

5) I've studied the example macros from TGaxis .html page, and they
haven't really helped, so can someone please answer my questions without
pointing to the example?  

Thanks, Mike

 Michael L. Miller
Yale Physics
michael.miller@yale.edu

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	Yale Software

Yale:   (203) 432-5637
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