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MathGroup Archive 1994

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Re: plots in reverse order

  • To: mathgroup at christensen.cybernetics.net
  • Subject: Re: plots in reverse order
  • From: Simon Chandler <simonc at hpcpbla.bri.hp.com>
  • Date: Mon, 17 Oct 1994 13:09:28 +0100

17/10/94

In my first bit of incomiing e-mail from the re-born MathGroup
(congratulations Steve, and hello again MathGroupies out there!) John
Pender said:

> on rare occasions I like to make plots for which the value of a point on the
> x axis decreases as you go from left to right, as opposed to increases.
> ... I haven't found an obvious solution

I have a similar problem with 2-D plots of _data_, like
ListContourPlot.  If I try to use MeshRange with 'reversed' labelling
of an axis then Mathematica 'automatically' switches around the
arguments I gave the MeshRange option; very frustrating.

My task was to produce a contour plot of a 2D matrix of data with the
x and y-axes labeled with numbers rather than the array values.  To do
this one usually uses ListContourPlot with the MeshRange option. i.e.,
I want to produce a plot of...


   100  1   2   3   4   5

   200  3   4   6   7   9

   300  4   7   8   6   5
    ^                             in this row are the
    |   10  20  30  40  50   <-- x-axis calibration values.
    |
    |
    \_  in this column are the y-axis calibration values.


I used:

   ListContourPlot[
      {{1,2,3,4,5},{3,4,6,7,9},{4,7,8,6,5}},
      MeshRange->{{10,30},{300,100}}
   ]

Note that the y-axis argument to MeshRange is {300,100}, with the
first element larger than the second.  This is because I wanted the
origin to be in the top left-hand corner as indicated.  However, this
produces an identical contour plot to:

   ListContourPlot[
      {{1,2,3,4,5},{3,4,6,7,9},{4,7,8,6,5}},
      MeshRange->{{10,30},{100,300}}
   ]

so you actually get


   300  1   2   3   4   5

   200  3   4   6   7   9

   100  4   7   8   6   5
    ^                             in this row are the
    |   10  20  30  40  50   <-- x-axis calibration values.  CORRECT 
    |
    |
    \_  in this column are the y-axis calibration values. WRONG


Effectively, MeshRange->{{10,50},{300,100}} becomes
MeshRange->{{10,50},{100,300}} before it is used to label the contour
plot.

My questions are:

* Why does MeshRange work in this way ?
* Is it supposed to ?
* How can I make my axis labels increase from the top left-hand corner ?

Thanks for your attention,

Simon

-----=----==---=-=--====-=---===--=--=-==-===-==--==-=-=-======--=-==--=

 Dr Simon Chandler
 Hewlett-Packard Ltd			Tel:   0272 228109
 Computer Peripherals Bristol		Fax:   0272 236091
 Filton Road, Stoke Gifford
 Bristol, BS12 6QZ	  		email: simonc at bri.hp.com
 United Kingdom

---==----=-=---====--=---=-==--===-=-=--=====-=----===---=--=--==-==-=-=









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