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Possible bug in Opacity[] with plotting function that uses UnitStep?

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  • Subject: [mg105593] Possible bug in Opacity[] with plotting function that uses UnitStep?
  • From: "Nasser M. Abbasi" <nma at 12000.org>
  • Date: Thu, 10 Dec 2009 04:57:46 -0500 (EST)
  • Reply-to: "Nasser M. Abbasi" <nma at 12000.org>

Version 7 on windows XP sp2.

This is really a strange one, it seems like a "bug", but if not, then what 
is it?

I have a function defined with UnitStep[]. I plot it using Plot and using 
Filling->Axis.

The filling works ok across all the plot range even with different 
FillingStyles for the color.

But when I use Opacity[] to change the filling Style more, then only _part_ 
of the plot is now affected by the Opacity[]  and the other part is not.

Compare the following 2 plots to see:

y = -400*UnitStep[x - 100.8] + 8*(x - 63.4)*UnitStep[x - 63.4]
     -8*(x - 43.2)*UnitStep[x - 43.2] + 221.3

Plot[y, {x, 0, 144},
          Filling -> Axis,
          FillingStyle -> {Opacity[0.5], Blue},
          Frame -> True]

Plot[y, {x, 0, 144},
         Filling -> Axis,
         FillingStyle -> Blue,
         Frame -> True]

--Nasser 



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