You are not running your loops correctly. If you ident your code (control-i) you can see better:
for i=1:1:N
while 1
x1=min(x)+(max(x)-min(x))*rand(1);
y1=min(y)+(max(y)-min(y))*rand(1);
z1=min(z)+(max(z)-min(z))*rand(1);
theta=2*pi*rand(1);
v=2*rand(1)-1;
x2=x1+L*sqrt(1-v^2)*cos(theta);
y2=y1+L*sqrt(1-v^2)*sin(theta);
z2=z1+L*v;
if x2<=x(2) && x2>=x(1) && y2<=y(2) && y2>=y(1) && z2<=z(2) && z2>=z(1)
break;
end
end
Fiber(i,1)=x1;
Fiber(i,2)=y1;
Fiber(i,3)=z1;
Fiber(i,4)=x2;
Fiber(i,5)=y2;
Fiber(i,6)=z2;
end
You have a for loop, pressumably to run N times (no need to do 1:1:N, with 1:N will work), then "while 1" does not have a condition to check, it will always enter (https://uk.mathworks.com/help/matlab/ref/while.html) and then an if in which you do not do anything. Finally, I do not think that you need a loop here, you are only adding random numbers to x1,y1,z1, most probably you could do what you want without the for loop.
