Fill gap created by Exclusions

Question

A gap appears at the locations of Exclusions at t=1,t=1+t0 when the top slider for t0 is set to Play. How can these gaps be avoided or filled in?

 Manipulate[  

 y[t_, t0_] := 1/(1 - (t - t0));  
 y0[x_] := y[x, 0];  
 yT[x_] := y[x, t0];  

 Plot[{y0[t], yT[t]}, {t, -3, 7},  
 Exclusions -> {t == 1, t == 1 + t0},  
 PlotStyle -> {{Thick, Black}},  
 PlotRange -> {0, 3},  
 Frame -> True,  
 Axes -> False,  
 ImageSize -> 1.2 {500, 330},  
 BaseStyle -> {FontSize -> 16},  
 FrameLabel -> {t, x},  
 RotateLabel -> False,  
 PlotRangePadding -> {{2, 0}, {.1, .1}},  
 Epilog -> {PointSize[0.015], Red, Dashed, 
 Line[{{-4, y0[s]}, {s, y0[s]}}],   
 Point[{{-4, y0[s]}, {s, y0[s]}, {s + t0, yT[s + t0]}}],  
 Black, Dashing[{}], Line[{{-4, 0}, {-4, 3}}],  
 Red, Point[{-4, y1[s]}],  
 Black, Arrowheads[.03], Arrow[{{-4, 3}, {-4, 3.1}}],  
 Red, Dashing[{}], Line[{{s, y0[s]}, {s + t0, yT[s + t0]}}]}],  

 {{t0, 2}, -2, 5, 0.01},  
 {{s, 0}, -2, 0.67, 0.01}   

 ]

Answer 1

I followed Mark McClure's suggestion concerning making two plots and combining them with Show, and it indeed fixes your gap problem.

Manipulate[
  Show[
    Plot[y0[t], {t, -3, 6.5},
      PlotRange -> {0, 3},
      PlotStyle -> {{Thick, Black}},
      Exclusions -> {t == 1}],
    Plot[yT[t], {t, -3, 6.5},
      PlotRange -> {0, 3},
      PlotStyle -> {{Thick, Black}},
      Exclusions -> {t == 1 + t0}],
    Frame -> True, Axes -> False,
    ImageSize -> 1.2 {500, 330},
    BaseStyle -> {FontSize -> 16},
    FrameLabel -> {"t", "x"},
    RotateLabel -> False,
    PlotRangePadding -> {{2, 0}, {.1, .1}},
    Epilog -> 
    {
      {Arrowheads[.03], Arrow[{{-4, 0}, {-4, 3}}]},
      {Red, PointSize[0.015], 
        Point[{{-4, y0[s]}, {s, y0[s]}, {s + t0, yT[s + t0]}, {-4, y1[s]}}]},
      {Red, Line[{{s, y0[s]}, {s + t0, yT[s + t0]}}], 
        Dashed, Line[{{-4, y0[s]}, {s, y0[s]}}]}
    }],
  {{t0, 2.}, -2., 5., 0.01, ImageSize -> Large},
  {{s, 0.}, -2., 0.67, 0.01, ImageSize -> Large},
  Initialization :> 
  (
    y[t_, t0_] := 1/(1 - (t - t0));
    y0[x_] := y[x, 0];
    y1[x_] := y[x, 1];
    yT[x_] := y[x, t0]
  )]

While I was at it, I rewrote your epilog to make it more logical and concise, and I introduced an initialization option so that your local functions are only defined once (in your code they are redefined every time the content pane is refreshed). I also made a guess about y1.

Answer 2

Combinining consecutive Lines into a single Line and moving the function definitions to Initialization (as suggested by @m_goldberg)

Manipulate[MapAt[# /. {x__, lines : Line[_] ..} :> {x,Line[Join @@ ({lines}[[All, 1]])]} &, 
  Plot[{y0[t], yT[t]}, {t, -3, 7},
       Exclusions -> 
       {t == 1, t == 0.5, t == 0.5 + t0, t == 1 + t0}, (* with few more exclusions *)
       PlotStyle -> {{Thick, Black}}, PlotRange -> {0, 3}, Frame -> True, 
       Axes -> False, ImageSize -> 1.2 {500, 330}, 
       BaseStyle -> {FontSize -> 16}, FrameLabel -> {t, x}, 
       RotateLabel -> False, PlotRangePadding -> {{2, 0}, {.1, .1}}, 
       Epilog -> {PointSize[0.015], Red, Dashed, 
                  Line[{{-4, y0[s]}, {s, y0[s]}}], 
                  Point[{{-4, y0[s]}, {s, y0[s]}, {s + t0, yT[s + t0]}}], Black, 
                  Dashing[{}], Line[{{-4, 0}, {-4, 3}}], Red, Point[{-4, yT[s]}], 
                  Black, Arrowheads[.03], Arrow[{{-4, 3}, {-4, 3.1}}], Red, 
                  Dashing[{}], Line[{{s, y0[s]}, {s + t0, yT[s + t0]}}]}], {1}] , 
  {{t0, 2}, -2, 5, 0.01}, {{s, 0}, -2, 0.67, 0.01}, 
  Initialization :> (y[t_, t0_] := 1/(1 - (t - t0));
                     y0[x_] := y[x, 0];
                     yT[x_] := y[x, t0])] 

Before (with Plot[...] instead of MapAt[..., Plot[...], ...]):

After: