<< RDL`ReactionDiffusionLab`
\(\(SetOptions[RDDensityPlots, 
        ColorFunction -> \((Hue[ .1,  .2 +  .8 \@ #\%4, 
                1 -  .95  #] &)\)];\)\)

actinhib := {a^2/b  -  a ,  a^2  -  b }

h = 1/50;
a0 = Table[Random[], {y, 0, 1, h}, {x, 0, 3/2, h}];
b0 = 
        Table[0.1  +  Random[], {y, 0, 1, h}, {x, 0, 3/2, 
            h}];

Da  =  0.0005;  Db  =  0.01;
dt =  .5*(h^2)/Max[{Da, Db}];

RDDensityPlots[actinhib, {a, b}, {a0, b0}, {Da, Db}, dt, 4, 
      PlotEvery -> 200, PlotRange -> {{0, 3}, {0, 3}}, 
      ImageSize -> 500]

Da  =  0.001;  Db  =  0.01;
dt =  .5*(h^2)/Max[{Da, Db}];

RDDensityPlots[actinhib, {a, b}, {a0, b0}, {Da, Db}, dt, 2, 
      PlotEvery -> 400, PlotRange -> {{0, 3}, {0, 3}}, 
      ImageSize -> 500]

Da  =  0.002;  Db  =  0.01;
dt =  .5*(h^2)/Max[{Da, Db}];

RDDensityPlots[actinhib, {a, b}, {a0, b0}, {Da, Db}, dt, 2, 
      PlotEvery -> 400, PlotRange -> {{0, 3}, {0, 3}}, 
      ImageSize -> 500]

RDSurfacePlots[actinhib, {a, b}, {a0, b0}, {Da, Db}, dt, 2, 
      PlotEvery -> 400, PlotRange -> {{0, 3}, {0, 3}}, 
      ImageSize -> 500]