Applications - A Guide to MATLAB for Beginners and Experienced Users - page 138

illumination. (See the online help for graph3d for more colormap options.)
ezcontourf(illum,[0 10 0 4]); colormap(gray);
axis equal tight

5) 2 +(y 2) 2 +9)

75/ π /((x − −

4

3.5

3

2.5

2

1.5

1

0.5

0

0 1 2 3 4 5 6 7 8 9 10

x

The darkest parts of the floor are the corners. Let us find the intensity of the
light at the corners, and at the center of the room.

subs(illum, {x, y}, {0, 0})
subs(illum, {x, y}, {5, 2})

ans =
0.6282
ans =
2.6526

The center of the room, at floor level, is about 4 times as bright as the
corners when there is only one bulb on the ceiling. Our objective is to light
the room more uniformly using more bulbs with the same total amount of
power. Before proceeding to deal with multiple bulbs, we observe that the
use of ezcontourf is somewhat confining, as it does not allow us to control
the number of contours in our pictures. Such control will be helpful in seeing
the light intensity; therefore we shall plot numerically rather than
symbolically; that is, we shall use contourf instead of ezcontourf .

Two 150-Watt Bulbs
In this case we need to decide where to put the two bulbs. Common sense
tells us to arrange the bulbs symmetrically along a line down the center of