| Re: RFC 1: Common functions for beginners [message #35150 is a reply to message #35080] |
Mon, 19 May 2003 16:35   |
condor
Messages: 35
Registered: January 2002
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Member |
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Ed Wright <ed.wright@jpl.nasa.gov> wrote in message news:<BAE813AB.B700%ed.wright@jpl.nasa.gov>...
> To: IDL guri
> From: Ed Wright
>
> I have a request for comments (just like the IETF).
>
> I learned the basics of IDL use and programming over a long time interval
> while writing the magnum opus of dlms. Rather than have new users repeat my
> learning process, I'd like your suggestions for the twenty or so most common
> IDL functions a new user should understand.
>
> I mean most basic-most used. Open file, read numbers, plot numbers, write
> text, close file.
>
> As always,
> Ed Wright
I think such alist would depend on the background of the user. Someone
mentioned that IDL counts from zero, which is important if you have a
fortran background but natural to someone who comes from C. (and could
go either way with someone who doesn't know any programming at all).
The 'format' for formatted output is trivial to the fortran guy, but
will stump the C-programmer. etc.
I wonder why nobody has mentioned indgen/findgen yet.
I also don't think anybody has mentioned plotting into a PS device.
Someone needs to spell out that there's two "help-functions", one is
called "?" and the other is called "help". Something like
"help,!P,/struct" can tell you where to start looking for something or
what to look for in the "?".
If people have any programming background at all, I'd hand them
"begin...end" as the basic grouping tool and mention that "end" can
often optionally be replaced with a more descriptive "endfor" or
"endif" and such and that this should be done. (I spent a year or two
blindly using 'if ... begin ... endif else begin ... endelse' without
knowing why IDL syntax for 'else' was so screwy, until someone told me
to think of the 'endif' and 'endelse' as 'end' and suddenly it's all
fairly trivial).
Integers are 16 bit! "Loop limit expression too large". 'Nuff said.
Many people mentioned "where" and it should include ",/count" so that
"if count gt 0 then ..."
The most common things in PLOT: psym=, thick=,
[xy]range=,/[xy]style,color=
[xy]title= vs. title= vs. subtitle=
a = indgen(20) & a[0:10] = (b = (a[5:15] = indgen(11)*3)) & print,a
; etc
When to ignore error messages (like Floating errors and such)
a = b+c/d ; if b,c and d are arrays of different dimensions.
Some word of warning about 'histogram'
I disagree that people need to know "device,decomposed=0" as this
already presumes a certain color model. Instead I'd introduce to
people the different color models and then direct them to something
that works for their machine (Some students are being placed in front
of a 5-year old Sparc box with 256 colors, some others have 24 (or
even 32-bit displays...) PLUS Some method to get a few clear,
well-known colors (red, green, blue, yellow) into their plot on screen
and in PS
Just what comes to my mind...
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