%% %% Ein Beispiel der DANTE-Edition %% %% 2. Auflage %% %% Beispiel 15-02-29 auf Seite 727. %% %% Copyright (C) 2016 Herbert Voss %% %% It may be distributed and/or modified under the conditions %% of the LaTeX Project Public License, either version 1.3 %% of this license or (at your option) any later version. %% %% See http://www.latex-project.org/lppl.txt for details. %% %% %% ==== % Show page(s) 1 %% defaultfont:="ptmr8r"; warningcheck:=0; % --- start of displayed preamble in the book --- % --- end of displayed preamble in the book --- % % beginfig(1) u=8mm; vardef project(expr x,y,z)=x*(-1,-1)+y*(1,0)+z*(0,1) enddef; vardef f(expr x,y)=sind((x/u)**2 *180 +(y/u)**2 *180)*u/2 enddef; numeric m,M,inc,farbe; m:=-2u; M:=2u; inc:=.1u; for i=m step inc until M: for j=m step inc until M: path p; p=project(i,j,f(i,j))--project(i,j+inc,f(i,j+inc))-- project(i+inc,j+inc,f(i+inc,j+inc))--project(i+inc,j,f(i+inc,j))--cycle; dfdx := (f(i,j) - f(i+inc,j))/inc; dfdy := (f(i,j) - f(i,j+inc))/inc; farbe := 1/sqrt( dfdx**2 + dfdy**2 + 1); fill p withcolor farbe*(red+green); endfor; endfor; endfig; end;