# point that are under line equation

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Mili Kian on 20 Apr 2020
Answered: Image Analyst on 21 Apr 2020
i have multi sentence equation and some point like this:
0<x<5 y=6
5<x<12 y=3x+6
12<x<15 y=-3x+7
15<x<20 y=6
and my points are(x,Y)
1 1
1 3
1 5
1 7
1 9
1 11
1 13
1 15
1 17
3 1
3 3
3 5
3 7
3 9
3 11
3 13
3 15
3 17
5 1
5 3
5 5
5 7
5 9
5 11
5 13
5 15
5 17
7 1
7 3
7 5
7 7
7 9
7 11
7 13
7 15
7 17
9 1
9 3
9 5
9 7
9 9
9 11
9 13
9 15
9 17
11 1
11 3
11 5
11 7
11 9
11 11
11 13
11 15
11 17
13 1
13 3
13 5
13 7
13 9
13 11
13 13
13 15
13 17
15 1
15 3
15 5
15 7
15 9
15 11
15 13
15 15
15 17
17 1
17 3
17 5
17 7
17 9
17 11
17 13
17 15
17 17
how can i find which point are under the equation

Michael Soskind on 20 Apr 2020
Hi Mili,
There are a few ways to go about this, I think the most obvious is the one I outline below:
% Redefining columns as x and y for clarity
x = C(:,1);
y = C(:,2);
% Conditions stated in question
cond_1 = x > 0 & x < 5 & y < 6;
cond_2 = x > 5 & x < 12 & y < 3*x + 6;
cond_3 = x > 12 & x < 15 & y < -3*x + 7;
cond_4 = x > 15 & x < 20 & y < 6;
% Selecting the points matching the conditions
points_below = C(cond_1 | cond_2 | cond_3 | cond_4, 1:2)
The method above assumes the array is called C. I redefine the columns into variables. I then use conditional statements that select for points matching the conditions above. NOTE: You may want to review the conditions you have in place, as they seem a bit strange to me, and maybe not what you are intending for.
However, the above should provide you with the final set of points as shown in the array points_below. Conditional statements are very powerful in Matlab.
Best,
Michael
Mili Kian on 21 Apr 2020
thank you
yes,as you said 'Conditional statements are very powerful in Matlab.'
best regard

Image Analyst on 21 Apr 2020