Page 182 - Basics of MATLAB and Beyond

N = 20;
dt = 2*pi/N;
t = 0:dt:(N-1)*dt;
x = [cos(t) cos(t)];
y = [sin(t) sin(t)];
z = [zeros(size(t)) ones(size(t))];

The matrix of vertices is
vert = [x’ y’ z’];
The matrix of faces must be defined so that each row gives, in order, the
indices of the vertices that we want to join. The first face is formed by
joining the vertices 1,N +1,N + 2 and 2; the second face is formed by
joining the vertices 2,N +2,N + 3 and 3; and so on. The faces matrix
therefore must have the form:
 
1 N +1 N +2 2
2 N +2 N +3 3
 
 
. . .
. . . .  .
 . 
 . . . .
 
N − 1 2N − 1 2N N
 
N 2N N +1 1
The faces matrix can be defined as follows:
faces = [1:N; N+1:2*N; [N+2:2*N N+1]; [2:N 1]]’;
We now have all the data we need to draw the patch:
clf 1
view(3)
z 0.5
h = patch(’vertices’,vert,...
’faces’,faces,’facecolor’,’y’); 1 0
1
xyz 0 0
y −1 −1 x
To colour the patch, we need to specify the temperature at each of the
vertices. We assume a heat source is located at (x, y, z)=(−.5, 0, 0.25),
and that the temperature at any point on the cylinder is inversely pro-
portional to its distance away from the source. The temperature at the
vertices is calculated as follows:

dist = sqrt((x + 0.5).^2 + y.^2 + (z - 0.25).^2);
T = 1./dist;
We can now do the patch colouring:

colormap(hot)
set(h,’facevertexcdata’,T’,...
’facecolor’,’interp’,...
’edgecolor’,’none’);

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