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Re: Epilog -vs- Prolog -vs- DisplayTogether

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  • Subject: [mg58110] Re: Epilog -vs- Prolog -vs- DisplayTogether
  • From: Bill Rowe <readnewsciv at>
  • Date: Sat, 18 Jun 2005 06:08:32 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

On 6/17/05 at 5:18 AM, noneya at (nafod40) wrote:

>Subject says it all. It is not clear to me the benefits of Epilog
>and Prolog over DisplayTogether, or when I'd use Epilog versus
>Prolog or vice versa. Mathematica book is kind of lean in that
>area. Anyone want to offer up some suggestions? What motivated
>their implementation in the first place?

The difference between Prolog and Epilog is when things are drawn. Also, directives used in Prolog and "leak", causing the later graphics to be drawn in a manner other than desired. Since Epilog occurs last, this "leakage" doesn't happen with Epilog.

For example, consider the following:

gr1 = Graphics[{Hue[0], Line[{{0, 0}, {1, 1}}]}]; 
gr2 = Graphics[{Hue[0], Line[{{0, 0}, {1, 1}}]}, 
    Prolog -> {Thickness[0.08], Circle[{0.2, 0.6}, 0.3]}]; 
gr3 = Graphics[{Hue[0], Line[{{0, 0}, {1, 1}}]}, 
    Epilog -> {Thickness[0.08], Circle[{0.2, 0.6}, 0.3]}]; 
gr4 = Graphics[
    {Thickness[0.08], Hue[0], Line[{{0, 0}, {1, 1}}]}, 
    Epilog -> {Thickness[0.08], Circle[{0.2, 0.6}, 0.3]}]; 
Show[GraphicsArray[{gr1, gr2, 
     gr3, gr4}]]; 

gr1 is simply a thin red line. 
gr2 adds a thick arc. Note the thickness of the red line as increased. Also, note the red line obscures part of the circle.
gr3 replaces Prolog with Epilog. Note the red line thickness is not increased.
gr4 inreases the thickness of the red line but uses Epilog to draw the circle. Compare this with gr2. Now part of the circle obscures a part of the red line.
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