Page 36 - Basics of MATLAB and Beyond

>> s = 100*spiral(3)
s =
700 800 900
600 100 200
500 400 300
>> ind = find(s>400)
ind =
1
2
3
4
7
>> s(ind)
ans =
700
600
500
800
900
>> s(s>400)
ans =
700
600
500
800
900
After introducing graphics of functions of two variables in the next sec-
tion, we will see how the find command can be used to do the three-
dimensional equivalent of the plot shown on page 23, where the domain
of a curve satisfying a logical test was extracted.

7 Graphics of Functions of Two Variables

7.1 Basic Plots
A matlab surface is defined by the z coordinates associated with a set
of (x, y) coordinates. For example, suppose we have the set of (x, y)
coordinates:
 
1, 12, 13, 14, 1
 1, 22, 23, 24, 2 
(x, y)=   .
 1, 32, 33, 34, 3 
1, 42, 43, 44, 4
The points can be plotted as (x, y) pairs:

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