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function hole3d()
// Holes in surfaces using %inf
// Copyright INRIA
t=linspace(-%pi,%pi,40);z=sin(t)'*cos(t);
z1=find(abs(z) > 0.5);
z(z1)=%inf*z1;
plot3d1(t,t,z);
function hole3d1()
// Holes in surfaces using %inf
deff('[x,y,z]=sph(alp,tet)',['x=r*cos(alp).*cos(tet)+orig(1)*ones(tet)';
'y=r*cos(alp).*sin(tet)+orig(2)*ones(tet)';
'z=r*sin(alp)+orig(3)*ones(tet)']);
r=1;orig=[0 0 0];
x=linspace(-%pi/2,%pi/2,40);y=linspace(0,%pi*2,20);
x(5:8)=%inf*ones(5:8);
x(30:35)=%inf*ones(30:35);
[x1,y1,z1]=eval3dp(sph,x,y);
plot3d1(x1,y1,z1)
function sphere
u = linspace(-%pi/2,%pi/2,40);
v = linspace(0,2*%pi,20);
x= cos(u)'*cos(v);
y= cos(u)'*sin(v);
z= sin(u)'*ones(v);
plot3d2(x,y,z);
function shell
u = linspace(0,2*%pi,40);
v = linspace(0,2*%pi,20);
x= (cos(u).*u)'*(1+cos(v)/2);
y= (u/2)'*sin(v);
z= (sin(u).*u)'*(1+cos(v)/2);
plot3d2(x,y,z);
function spiral
[r,a]=field(0:0.1:1,0:%pi/8:6*%pi);
z=a/8;
x=r.*cos(a).*(1-a/20);
y=r.*sin(a).*(1-a/20);
z=z-1.5;
plot3d2(x,y,z);
function rings
rr=0.2;
t=linspace(0,2*%pi,10);
s=linspace(0,2*%pi,41); n=length(s);
r=dup(1+cos(t)*rr,n)'; m=length(t);
x=dup(cos(s),m).*r; y=dup(sin(s),m).*r;
z=dup(sin(t)*rr,n)';
X=[x;(x+1.3);(x-1.3)];
Y=[y;-z;-z];
Z=[z;y;y];
plot3d2(X,Y,Z,[m,2*m]);
function torus
// some torus type bodies.
x=linspace(0,2*%pi,40);
y=linspace(0,2*%pi,20)';
// a torus with a thick and a thin side.
factor=1.5+cos(y)*(cos(x)/2+0.6);
X=factor*diag(cos(x));
Y=factor*diag(sin(x));
Z=sin(y)*(cos(x)/2+0.6);
plot3d2(X,Y,Z);
function torus1
// a deformed torus
x=linspace(0,2*%pi,40);
y=linspace(0,2*%pi,20)';
factor=1.5+cos(y);
X=factor*cos(x);
Y=factor*sin(x);
Z=sin(y)*ones(x)+ ones(y)*cos(2*x);
plot3d2(X,Y,Z);
function moebius
// the Moebius band
t=linspace(-1,1,20)';
x=linspace(0,%pi,40);
factor=2+ t*cos(x);
X=factor*diag(cos(2*x));
Y=factor*diag(sin(2*x));
Z=t*sin(x);
plot3d2(X,Y,Z);
function tube(nn)
// some tube like bodies.
x=linspace(0,2*%pi,nn);
// atomic modell or so.
y=0.1+[sin(linspace(0,%pi,15)),1.5*sin(linspace(0,%pi,10)),sin(linspace(0,%pi,15))];
cosphi=dup(cos(x),length(y));
sinphi=dup(sin(x),length(y));
f=dup(y',length(x));
x1=f.*cosphi; y1=f.*sinphi;
z=dup(linspace(-2,2,prod(size(y)))',prod(size(x)));
plot3d2(x1,y1,z,-1,35,70);
function bh(nn)
// a black hole
x=linspace(0,2*%pi,nn);
t=linspace(0,1,20);
cosphi=dup(cos(x),length(t));
sinphi=dup(sin(x),length(t));
f=dup((t.*t+0.2)',length(x));
plot3d2(f.*cosphi,f.*sinphi,dup(t'.*2-1,length(x)));
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