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Re: extract elements from a list

  • To: mathgroup at
  • Subject: [mg2850] Re: extract elements from a list
  • From: NEWSMGR at
  • Date: Wed, 27 Dec 1995 00:48:03 -0500
  • Organization: Southeastern Louisiana University

>Subject: Re: extract elements from a list
>From: koppel at (David M. Koppelman)
>Organization: Louisiana State University ECE Dept.

In article <4bg3ba$ob8 at> "cjkelly at" <cjkelly at> writes:

> I've been trying to extract elements from a list x={a,b,c,d,e...}
> then square each value and pair it up with the original unsquared value.
> These two values form a point (2Dim) and I then try to pair up each
> point with a given vertex of {5,25} and use Line[{{5,25},{a,a^2}}] to
> graph this thing.
> My main routine (reAlly kinda small)
> is...Do[n=x[[i]];Line[{{5,25},{n,n^2}}],{i,10,1}]
> When this is run nothing happens....
> in this case x={5,5.5,5.4,5.3,5.2...ect}

There are several problems with the code above. First, a negative step
should be used when iterating from 10 to 1. (Unless that was a typo.)
The "Line" function doesn't draw a line when evaluated.  Instead,
"Line" is meaningful as an argument to "Graphics."  Similarly,
evaluating "Graphics" does not result in anything being drawn; it
should be used as an argument to "Show" which will draw the stuff
described by "Graphics."

The following might do what you want:


> I've been stuck for 2 weeks unable to get this to work and it is
> driving me crazy because it should be sooo easy.  

One has not really experienced frustruation until one has worked
with computers.

      /\                                /\                              /\
      <>                                <>  David M. Koppelman          <>
      <>        koppel at  <>  102 EE Building             <>
      <>                (504)-388-5482  <>  Louisiana State University  <>
      <>  <>  Baton Rouge, La 70803       <>
      ~~                                ~~                              ~~

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