Asked by Mounisha Ganesan
on 10 Jul 2019

I have a for loop where I initiialize random values to variables and I check for certain condition, if my condition is not met I have to reinitialize the values for the same iteration. How do I do so?

Here's a sample

n = 100;

for i = 1:n

x(i) = rand

y(i) = rand

if(x(i)< 0 || y(i)<0)

disp(' I need to reinitialize values for the same i and my n count should be 100')

end

end

So I have to run the loop until I reach my 'n' value and meet my conditions within the loop. Is there a way to do it or should I use different loop like while?

Answer by infinity
on 10 Jul 2019

Edited by infinity
on 10 Jul 2019

Accepted Answer

Hello,

There are several ways, one approach that you can use as follows

clear

n = 100;

x = zeros(1,n);

y = zeros(1,n);

for i = 1:n

xt = rand;

yt = rand;

while (xt*yt<0)

xt = rand;

yt = rand;

end

x(i) = xt;

y(i) = yt;

end

infinity
on 10 Jul 2019

Hello,

"I would like to know why do we have to use * operator instead of || operator. It means when one value is less than zero the product automatically becomes less than zero? Am I right? "

I can use * operator is because it is equivalent with your condition x < 0 || y < 0. If one of them (x and y) less than 0 then x * y < 0 and inverse.

Also, as you can see that x*y < 0 is shorter than (x< 0 || y < 0). But, of course, you can use your original condition.

"And what should I do if I have to check two conditions say I have to new variables x2t and y2t which depensds on xt and yt are always between (0 and 1) in this code given below

Is my code right?"

Actually, what I have done before are not necessary since function "rand" generate a real random number between 0 and 1. Therefore, now you don't need to use condition to on xt and yt.

But for your current problem, x2 and y2 can be negative and can be greater than 1. Therefore, you should implement conditions and the code could be like

a = 0;

b= 1;

l = 0.2;

for i = 1:n

x1(i) = a + (b-a)*rand;

y1(i) = a + (b-a)*rand;

thetax = 2*pi*rand;

thetay = 2*pi*rand;

x2next = x1(i) + li(i)*cos(thetax);

y2next = y1(i) + li(i)*sin(thetay);

while (x2next < 0 || x2next > 1)

thetax = 2*pi*rand;

x2next = x1(i) + li(i)*cos(thetax);

end

while (y2next < 0 || y2next > 1)

thetay = 2*pi*rand;

y2next = y1(i) + li(i)*sin(thetay);

end

x2(i) = x2next;

y2(i) = y2next;

end

I have put a, b and l out side the loop since they are constants.

More details of function "rand" can be found by typing

help rand

Mounisha Ganesan
on 10 Jul 2019

infinity
on 10 Jul 2019

Hello,

I got your point. You can see my comment above, which is just modified.

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