Picking random points...

Hi

I am exploring a closed (time) interval between 0 and 1. I have used the linspace command to generate it:

t=linspace(0,1);

I can't seem to figure out how to randomly pick 10 (say) of these points in t so that I can plug them into a function (selected in a non-uniform way). Any thought?

Many thanks

Joe

Answer 1

[Stephen23]

You can simply generate some indices to pick value from the vector t. I have shown you uniformly distributed random indices, because you did not tell us what random distribution you want. Two solutions are shown below: without and with index repetition.

t = linspace(0,1);
N = 5; % how many points to pick

Without repetitions use randperm:

>> idx = randperm(numel(t),N)
idx =
   45   75   58   51   15
>> t(idx)
ans =
   0.44444   0.74747   0.57576   0.50505   0.14141

With repetitions use randi:

>> idy = randi(numel(t),1,N)
idy =
   53   44   11   77   71
>> t(idy)
ans =
   0.52525   0.43434   0.10101   0.76768   0.70707

[Joe Bannen]

Stephen

Thanks for this. I am looking for an interval with non uniform nodes to use in my equation. How would this change things?

Cheers

Joe

[Stephen23]

Define your interval and distribution, and use these to generate some indices, exactly as I have shown.

Do you know which distribution you need?

[Joe Bannen]

Stephen

I think you were correct in the first answer, it is my lack of understanding that is causing the problem.

I had been using:

    t_1=rand(10,1);

But now need to randomly pick 10 items from:

t=linspace(0,1);

Since randn uses the standard normal distribution, your suggestion should work! Please let me know if I am wrong on this.

Best wishes

Joe

[Thorsten]

Maybe you want to sort the 10 randomly picked numbers:

 t=linspace(0,1);
 t10 = t(sort(randperm(numel(t), 10)))