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| Re: Plotting functions in IDL [message #5619 is a reply to message #5513] |
Fri, 19 January 1996 00:00  |
rivers
Messages: 228
Registered: March 1991
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Senior Member |
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In article <4dgftr$1qr5@rs18.hrz.th-darmstadt.de>, kunstman@pu.informatik.th-darmstadt.de (Thomas Kunstmann) writes:
> What is the best way of plotting a function in IDL? As far as I know,
> it only handles vectors of discrete data and no equations.
>
I think what he is asking is whether IDL can plot "expressions" or "equations"
which are not known at the time a procedure is written, but rather are
determined at run time.
This is indeed possible in IDL, using the EXECUTE function. Here is an example
of an IDL program which does so, and the output of a session using it.
************************************************************
print, 'Enter expression to be plotted'
expression=''
read, expression
t = execute('plot, '+expression+', title=expression')
end
************************************************************
; IDL Version 4.0.1 (vms alpha)
; Journal File for CARS3::RIVERS
; Working directory: USER_DISK:[RIVERS.IDL]
; Date: Fri Jan 19 16:51:12 1996
.run test_plot
;Enter expression to be plotted
; sin(findgen(100)/10.)
The procedure then draws the plot of the user-entered expression.
____________________________________________________________
Mark Rivers (312) 702-2279 (office)
CARS (312) 702-9951 (secretary)
Univ. of Chicago (312) 702-5454 (FAX)
5640 S. Ellis Ave. (708) 922-0499 (home)
Chicago, IL 60637 rivers@cars3.uchicago.edu (Internet)
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| Re: Plotting functions in IDL [message #5635 is a reply to message #5513] |
Thu, 18 January 1996 00:00 |
hahn
Messages: 108
Registered: November 1993
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Senior Member |
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kunstman@pu.informatik.th-darmstadt.de (Thomas Kunstmann) wrote:
> What is the best way of plotting a function in IDL? As far as I know,
> it only handles vectors of discrete data and no equations.
Yes, IDL need the data in tables, either in core or on disk.
Actuall, I'm glad that this avoids error, because you have to
think of how to fill the table. I.e. try the following with
mathematica:
Plot[Sin[x*x],{x,-3Pi,3Pi}]
you won't believe your eyes!
What mathematica does - and many other packages do - is to divide the
given intervall into equal pieces and call the function at the pivots.
But due to the periodicy and due to rounding errors the function
are neither symmectrical to the y axis nor are the extremes always
found. Thus in this case you have a dip in the amplitude at x=7.1.
The minimum y value is -0.3 rather than -1.
So you either think of how to fill the table that IDL should plot or
use some other graphics package and believe the results!
Norbert Hahn
TH Darmstadt
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| Re: Plotting functions in IDL [message #5643 is a reply to message #5513] |
Thu, 18 January 1996 00:00 |
korpela
Messages: 59
Registered: September 1993
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Member |
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In article <4dgftr$1qr5@rs18.hrz.th-darmstadt.de>,
Thomas Kunstmann <kunstman@pu.informatik.th-darmstadt.de> wrote:
> What is the best way of plotting a function in IDL? As far as I know,
> it only handles vectors of discrete data and no equations.
First set up a range and then plot the function over the range.
The way I do it is, for example....
IDL> x=range(-3.*!pi,3.*!pi,0.01)
% Compiled module: RANGE.
IDL> plot,x,sin(x*x)
I have a function called range that looks like this.....
------------------------------------------------------------ ------------
Function range,lo,hi,delta
if (n_params(0) lt 2) or (n_params(0) gt 3) then begin
print,'RANGE-- Incorrect number of parameters'
return,-9999.0
endif
if (n_params(0) eq 2) then delta=1.0
number=long((float(hi)-float(lo))/float(delta))
outrange=float(lo)+findgen(number)*float(delta)
return,[outrange,hi]
end
------------------------------------------------------------ ------------
Eric
--
Eric Korpela | An object at rest can never be
korpela@ssl.berkeley.edu | stopped.
<a href=" http://www.cs.indiana.edu/finger/mofo.ssl.berkeley.edu/korpe la/w">
Click here for more info.</a>
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