> #sfb tanplane.mws 6 feb 03
> #
> with(plots):with(plottools);
> f:=x^2+y^2;#f:=sin(x)*sin(y);f:=exp(-x^2-y^2);
> fstring:=convert(f,string);ftitle:="The good doctor's "||fstring;
> a:=0.3;
> b:=0.5;
> c:=eval(f,{x=a,y=b});
> L:=1;
> A:=plot3d(f,x=a-L..a+L,y=b-L..b+L,style=patchcontour,contours=[seq(c-L+i*L/5,i=1..9)],axes=boxed,view=[a-L..a+L,b-L..b+L,c-L..c+L],title=ftitle):A;
> P:=sphere([a,b,c],L/50,color=black):
> display(A,P);
> fx:=diff(f,x);fy:=diff(f,y);
> fxP:=eval(fx,{x=a,y=b});fyP:=eval(fy,{x=a,y=b});
> ftanP:=fxP*(x-a)+fyP*(y-b)+c;
> T:=plot3d(ftanP,x=a-L..a+L,y=b-L..b+L,style=patchcontour,contours=[seq(c-L+i*L/5,i=1..9)],axes=boxed,view=[a-L..a+L,b-L..b+L,c-L..c+L],shading=zhue):
> display(A,P,T);
>