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Re: plot a function using solid line between [-pi, pi] while dashed line extended a little on both side

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From	Ingo Thies <ingo.thies@gmx.de>
Newsgroups	comp.graphics.apps.gnuplot
Subject	Re: plot a function using solid line between [-pi, pi] while dashed line extended a little on both side
Date	Mon, 26 Dec 2011 09:36:13 +0100
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Hello Steven and happy Christmas!

> I need to draw a -sinx function using solid line between [-pi, pi]
> while dashed line extended.   The dashed line to show that the
> function will be extended infinitely on both side, not stopped from -
> pi  to pi.

I am not up to date whether gnuplot now has an intrinsic option for 
that. However, the standard solution has ever been to define two 
truncated functions. Let sin(x) be your function to be plotted. Then define

fin(x) = abs(x)<=pi ? sin(x) : 1/0
fout(x)= abs(x)>pi  ? sin(x) : 1/0

For the full description, see the gnuplot.pdf and look for "ternary" in 
the "Operators" section (p.29 in my version, but varies a little due to 
updates of the document).

The term 1/0 gives an unplottable value which ist simply skipped by 
gnuplot. Nowadays, also NaN (not a number) can be used directly. Now 
plot as follows (I skipped your other definitions here):

plot fin(x) w l lt 1, fout(x) w l lt 2

Instead of linetypes 1 and 2 you can, of course, also define linestyles, 
one with solid (linetype 1), and one with dashed (lt 2) shape. If all 
plots are the same colour and the dashed line is not wider than the 
solid one (i.e. it will be hidden by the solid line), you can skip the 
definition of fout entirely and use your sin(x) function directly.

HTH,

Ingo

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plot a function using solid line between [-pi, pi] while dashed line extended a little on both side Steven Du <stevendduu@gmail.com> - 2011-12-25 21:36 -0800
  Re: plot a function using solid line between [-pi, pi] while dashed line   extended a little on both side Ingo Thies <ingo.thies@gmx.de> - 2011-12-26 09:36 +0100
    Re: plot a function using solid line between [-pi, pi] while dashed line extended a little on both side Steven Du <stevendduu@gmail.com> - 2011-12-26 22:09 -0800

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