Troubleshooting - A Guide to MATLAB for Beginners and Experienced Users - page 224

Error in ==> /usr/matlabr12/toolbox/matlab/graph3d/mesh.m
On line 68 ==> hh = surface(x, , FaceColor , ,fc, , EdgeColor , ,
, flat , , , FaceLighting , , , none , , , EdgeLighting , , , flat , );

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Figure11-1

These error messages indicate that you have tried to plot the wrong kind of
object, and that's why the figure window (Figure 11-1) is blank. What's wrong
in this case is evident from the first error message. While you might think

you can plot the hemisphere z = 1 − x 2

− y 2 this way, there are points in the

domain − 1 ≤ x , y ≤ 1 where 1 − x 2

− y 2 is negative and thus the square root
is imaginary. But mesh can't handle complex inputs; the coordinates need to
be real. One can get around this by redefining the function at the points where
it's not real, like this:
>> [X,Y] = meshgrid(-1:.1:1, -1:.1:1);
>> mesh(X, Y, sqrt(max(1 - X.ˆ2 - Y.ˆ2, 0)))
The output is shown in Figure 11-2.

A Previously Saved M-File Evaluates Differently
One of the most frustrating problems you may encounter occurs when a
previously saved M-file, one that you are sure is in good shape, won't eval-
uate or evaluates incorrectly, when opened in a new session.