Page 46 - Basics of MATLAB and Beyond

>> z = 5*ones(3,3)
z = 6
5 5 5 5.5
5 5 5 5
5 5 5 4.5
>> surf(x,y,z) 4
3
2 1
1 0
0 −1
But, of course, the z values need not be constant:
>> z = [[4; 5; 6] [4.5; 5; 5.5] [4.9; 5; 5.1]]
z =
4.0 4.5 4.9
5.0 5.0 5.0 6
6.0 5.5 5.1 5.5
>> surf(x,y,z) 5
4.5
4
3
1
2
1 0
0 −1
Other graphics functions can also handle nonrectangular grids. Here is
an example using the contour function:
3
5.8
2.5 5.6
cs = contour(x,y,z,’k’);
2
clabel(cs) 5 5.4
4.8
1.5
i=[1479631]; 4.4 5.2
4.2
hold on 1 4.6
plt(x(i),y(i),’:’) 0.5
0
−1 −0.5 0 0.5 1
The contour levels are labelled using the clabel command, and the
region defined by the x and y points is outlined by the dotted line. The
contours that the labels refer to are marked by small plus signs ‘+’. The
outline around the bent domain is drawn using the x and y matrices
indexed using the vector i. The vector i extracts the appropriate points
from the x and y matrices using the columnar indexing described in sec-
tion 3.4 on page 9. The other surface graphics functions—mesh, surfl,
surfc, and contourf—can handle such nonrectangular grids equally
well. The image and imagesc functions assume equally spaced rect-
angular grids and cannot handle anything else. (The pcolor function
draws a surface and sets the view point to directly overhead, so it is not
discussed separately.)
Let us now do another example of a surface defined over a non-
rectangular grid. We want to define a set of points that cover the semi-

c 2000 by CRC Press LLC