Question

I would like to create a notebook with a demonstration:

SlopeInterceptDemonstration[{mmin_, mmax_}, {bmin_, bmax_}] :=
Module[{xmax, xmin},
xmax = Max[Abs[bmin + mmin], Abs[bmax + mmax]]*1.2;
xmin = - xmax;

Manipulate[
        Plot[m*x + b, {x, xmin, xmax}, AspectRatio -> 1, PlotRange -> {xmin, xmax}],
        {{m, mmin, "m"}, mmin, mmax, 0.1}, {{b, bmin, "b"}, bmin, bmax, 0.1}]
];

If I save a notebook with a simple call ( SlopeInterceptDemonstration[{-2, 2}, {-5, 5}] ) evaluated and reopen it with a fresh kernel the demo is not displayed because xmin and xmax are not known.

Is there a way force the evaluation of these variables inside Plot?

Answer 1

You can use DynamicModule together with the SaveDefinitions option in Manipulate :

SlopeInterceptDemonstration[{mmin_, mmax_}, {bmin_, bmax_}] := DynamicModule[{xmax, xmin}, 
  xmax = Max[Abs[bmin + mmin], Abs[bmax + mmax]]*1.2;
  xmin = -xmax;
  Manipulate[Plot[m*x + b, {x, xmin, xmax}, AspectRatio -> 1, 
   PlotRange -> {xmin, xmax}], {{m, mmin, "m"}, mmin, mmax, 0.1}, {{b, bmin, "b"}, bmin, bmax, 0.1}, 
   SaveDefinitions -> True]]