Re: Possible bug in Opacity[] with plotting function that uses UnitStep?
- To: mathgroup at smc.vnet.net
- Subject: [mg105595] Re: Possible bug in Opacity[] with plotting function that uses UnitStep?
- From: "Nasser M. Abbasi" <nma at 12000.org>
- Date: Thu, 10 Dec 2009 04:58:09 -0500 (EST)
- Reply-to: "Nasser M. Abbasi" <nma at 12000.org>
----- Original Message -----
From: "Nasser M. Abbasi" <nma at 12000.org>
To: <mathgroup at smc.vnet.net>
Sent: Wednesday, December 09, 2009 7:42 PM
Subject: [mg105595] Possible bug in Opacity[] with plotting function that uses
UnitStep?
> 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
FYI;
I have found how to do it. The trick is to use Opacity[.5,Blue] and NOT
{Opacity[0.5], Blue}
The following now works as expected.
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[.5,Blue],
Frame -> True]
Plot[y, {x, 0, 144},
Filling -> Axis,
FillingStyle -> Blue,
Frame -> True]
I think writing {Opacity[0.5], Blue} instead of Opacity[.5,Blue] made it
use the blue part for one part of the plot and Opacity[0.5] for another
part.
One more item added to my Mathematica cheat sheet.
--Nasser