How to generate just one random number in every iteration of for loop?

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hamed 2014-7-27

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评论： hamed 2014-7-27

I want to generate n random number in a For loop from 1:n. But, every time as the loop iteration increase the number of generated points would increase as well. I need to generate just one pair(x,y) random number in every iterations.

For i=1:10;
%generate a random x,y
x(i)=rand(1)
y(i)=rand(1)
if x(i)<0.01 && y(i)<0.5
%generate another random x,y and make comparison again
x(i)=rand(1)
y(i)=rand(1)
return
end
end
%For example when i=4 this code generate 4 random x,y which is not my favorite i want just another single x,y

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Answer 1

Image Analyst 2014-7-27

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https://ww2.mathworks.cn/matlabcentral/answers/143481-how-to-generate-just-one-random-number-in-every-iteration-of-for-loop#answer_146532

在 MATLAB Online 中打开

I think you want

if x(i) < 0.01 && y(i) < 0.5

instead of

if x<0.01 && y<0.5

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Image Analyst 2014-7-27

在 MATLAB Online 中打开

Why not? Each iteration will generate one pair. Some percentage of the time the "if" statement will be true and the pair will be replaced by a different pair, but at the end, you still have one pair (an x and a y) for each iteration. As far as I can tell that meets your needs of "I need to generate just one pair(x,y) random number in every iterations." If it doesn't, say WHY it doesn't rather than just say "it's not my answer."

I see you took my advice and edited your code to include my code. The only thing I fixed was converting For to lower case and adding a printout of x and y, and correcting the indentation, and I got this code:

for i=1:10;
  %generate a random x,y
  x(i)=rand(1)
  y(i)=rand(1)
  if x(i)<0.01 && y(i)<0.5
    %generate another random x,y and make comparison again
    x(i)=rand(1)
    y(i)=rand(1)
    return
  end
end
x
y
whos x
whos y

You'll see this:

   Name      Size            Bytes  Class     Attributes
    x         1x10               80  double              
    Name      Size            Bytes  Class     Attributes
    y         1x10               80  double

so you can see that this proves x and y are 10 elements long, and 10 is the number of iterations. So please explain why my fix is not working.

dpb 2014-7-27

在 MATLAB Online 中打开

If perhaps I read between the lines maybe I finally begin to get the underlying question -- if you write (no loop, no nothing already in existence)

k=2;
x(k)=rand(1);

the resulting length(x) will be 2 because Matlab doesn't have variable lower indices on arrays - it will fill in x(1)=0 in the above. There aren't two random values, only one of those, but the size(x) will reflect the upper bounds of the array index used.

If that is the symptom of which your complaining, don't create the index at all--if it's only one value you don't need an array at all, anyway; just use

x=rand(1);

overwriting the previous value.

Other than that I have no klew what the complaint is; try again if that isn't it.

hamed 2014-7-27