Randomly chooses points from a triangular region and stores the x and y coordinates

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Sophie Culhane
Sophie Culhane 2020-10-12
回答： Asad (Mehrzad) Khoddam 2020-10-13
My task is to write a MATLAB function where b and h are positive real numbers, n is a positive integer, and x and y are row vectors of length n. Program will randomly choose n points from the triangular region having vertices (0,0), (b, 0) and (b,h) and stores the x-coordinates and y-coordinates of the n points in the x and y vectors respectively in the order the points are chosen. I have a program written out that produces y-values, but I am not sure how to get both x and y values from the program.
Here is what I have so far:
function [x,y] = hw22(b,h,n)
%
rng('shuffle')
x = zeros(1,n);
y = zeros(1,n);
k = 1;
while k <= n
x(k) = h*rand;
y(k) = b*rand;
if y(k) < b/h*x(k)
k = k + 1;
end
end
  1 个评论
Sophie Culhane
Sophie Culhane 2020-10-12
For each random point, keep the random point if it is in the triangular region having vertices (0,0), (b,0) and (b,h), and if the random point is not in the triangular region, preform the appropriate transformation on the point to create a point that is in the triangular region.

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回答（5 个）

Asad (Mehrzad) Khoddam
function [x,y] = hw22(b,h,n)
%
rng('shuffle')
x = zeros(1,n);
y = zeros(1,n);
k = 1;
while k <= n
xr = h*rand;
yr = b*rand;
if yr < b/h*xr
x(k)=xr;
y(k)=yr;
k = k + 1;
end
end
Ameer Hamza
Ameer Hamza 2020-10-12
编辑：Ameer Hamza 2020-10-12
The code seems correct, just swap the h and b
[x, y] = hw22(1, 2, 1000);
plot(x, y, '+');
function [x,y] = hw22(b,h,n)
%
rng('shuffle')
x = zeros(1,n);
y = zeros(1,n);
k = 1;
while k <= n
x(k) = b*rand;
y(k) = h*rand;
if y(k) < h/b*x(k)
k = k + 1;
end
end
end
Also read about impolygon(): https://www.mathworks.com/help/matlab/ref/inpolygon.html
Bruno Luong
Bruno Luong 2020-10-12
编辑：Bruno Luong 2020-10-12
This is a direct method, no loop, no discard, etc...
n = 1e4;
b = 1;
h = 2;
w1=1-sqrt(rand(1,n));
w2=(1-w1).*rand(1,n);
w3=1-(w1+w2);
w=[w1;w2;w3];
% triangle coordinates
Txy =[0, b, b;
0, 0, h];
Rxy = Txy*w;
x = Rxy(1,:);
y = Rxy(2,:);
% Check
plot(x,y,'.')
Asad (Mehrzad) Khoddam
function [x,y] = hw22(b,h,n)
x=rand(n,1)*b;
y=rand(n,1).*x*h/b;
end
Asad (Mehrzad) Khoddam
function [x,y] = hw22(b,h,n)
x=rand(n,1)*b;
y=rand(n,1)*h;
ind=find(y>x*b/h);
x(ind)=b-x(ind);
y(ind)=h-y(ind);
end

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