Advice: Plotting a sequence of points

Suppose you want to produce a plot by generating points one at a time, and plotting them. In a typical programming language such as C, you would probably build up the plot one point at a time, plotting each point as it is generated. This is not the way Maple works, however. In Maple a plot is a single object, whose image on the screen or in a file is "printed" as the result of one command (although this may use the results of several different plot commands, combined with display ).

To plot a sequence of points, you build up a list or array of points and then plot it. In the case of a large list, an array can be more efficient. To take maximum advantage of the speed of hardware floating-point arithmetic, you can use an hfarray. However, this can not be plotted directly, but should be converted to a list of lists using convert(..., listlist) . It is also faster to use pointplot in the plots package rather than plot with the style=POINT option. For a three-dimensional plot, use pointplot3d in the plots package.

Use the option symbol=POINT when plotting points to make each point be a single dot. The other possibilities are BOX , CIRCLE , CROSS and DIAMOND (which is the default). Or you can join the points with lines using pointplot or pointplot3d with the option style=LINE .

Example:

Here we generate a plot of 4000 successive points of the Hénon map . To take maximum advantage of the speed of hardware floating-point arithmetic, we write a procedure to compute the points and put them in an hfarray, and evaluate it using evalhf .

> makearray:= proc()
   local L, i, x, y, xp;
   L := hfarray(1 .. 4000,1 .. 2);
   x:= 0.6; y := 0.2;
   for i to 400 do
      xp := 1+y-1.4*x^2;
      y := .3*x;
      x := xp;
   od;
   for i to 4000 do
      xp := 1+y-1.4*x^2;
      y := .3*x;
      x := xp;
      L[i,1]:= x; L[i,2]:= y;
   od;
   L
  end:

> L:= evalhf(makearray()):

Now we convert the hfarray to a list of lists, and use pointplot to plot it.

> Ll:= convert(L,listlist):

> plots[pointplot](Ll,symbol=POINT);

See also:

evalhf , hfarray , convert(listlist) , plot , plot(options) , pointplot , pointplot3d

Maple Advisor Database, R. Israel 1998