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| From | Bill Rowe <readnews@sbcglobal.net> |
| Newsgroups | comp.soft-sys.math.mathematica |
| Subject | Re: vs. f[a]. When are they equal? |
| Date | Wed, 27 Apr 2011 09:38:14 +0000 (UTC) |
| Organization | Steven M. Christensen and Associates, Inc and MathTensor, Inc. |
| Sender | steve@smc.vnet.net |
| Approved | Steven M. Christensen <steve@smc.vnet.net>, Moderator |
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| NNTP-Posting-Date | 27 Apr 2011 08:38:58 GMT |
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On 4/26/11 at 4:43 AM, fateman@cs.berkeley.edu (Richard Fateman) wrote:
>Here's a fun thing to do with our function f[x_]:=1/(1-Exp[I x]) .
>try Plot[Re[f[x]],{x,0.01,20}]
>On my system it look like a plot of y=0. A bug (Mathematica 7)?
Look closely at a plot of y = 0 and you will see that it is
different from a plot of f[x] above. The difference is much more
obvious if you move the origin for the axes. That is
Plot[0 , {x, .01, 20}, AxesOrigin -> {0, .5}]
is clearly different from
Plot[f[x], {x, .01, 20}, AxesOrigin -> {0, .5}]
Nothing at all is being plotted when you attempt to plot f[x].
This is not a bug since Plot is designed to plot functions where
they have real values. Doing
Plot[Im[f[x]], {x, .01, 20}, AxesOrigin -> {0, .5}]
shows the function has real values at regularly spaced points.
The likelihood of Mathematica selecting these points when
evaluating f[x] is essentially zero. Consequently, Plot all plot
sees as values for f[x] are complex values which are not plotted.
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Re: vs. f[a]. When are they equal? Bill Rowe <readnews@sbcglobal.net> - 2011-04-27 09:38 +0000
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