How To Generate Non Repeating floating Random Numbers from 1 to 10

Hi,

Does anybody know how to generate a series of 100 non-repeating random floating numbers between 1 and 10?

Thanks

Answer 1

[Star Strider]

One option:

v = rand(1, 100)*9+1;
[L, H] = bounds(v)                         % Check

producing (in this run):

L =
     1.0846

H =
     9.9740

[Walter Roberson]

This code does not strictly guarantee that the values will be non-repeating. In practice, though, I have never seen duplicate rand() values show up except when I manipulated the random number seed.

[Star Strider]

I also have never seen them repeat. I tested that at one point by using unique:

Check = numel(unique(v))

This has always been the same as numel(v) when I have tried it.

[Walter Roberson]

I just did a test with 5e8 and got back 5e8 minus 9 unique, so it can happen with large enough arrays.

[Star Strider]

With a pseudo-random random number generator, I’m certain that’s possible. With a vector of only 100 numbers, several trials (in a loop) have always found equality between the element numbers of the vector and its unique elements, although with enough trials, there are bound to occasionally be repeats. Noting that is a probability of , so it is not likely to be a significant issue with a vector of 100 elements.

[Walter Roberson]

With 2^53 possible rand() outputs, an estimation using The Birthday Paradox logic suggests that the probability of a duplicate rises to 1/2 at about 10^8

[Star Strider]

Noted.

I’d not thought to test this with the ‘Birthday Party’ problem.

Answer 2

[Andrei Bobrov]

z = cumsum(rand(100,1));
mn = min(z);
Z = 9/(max(z) - mn)*(z - mn) + 1;
out = Z(randperm(100));