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Picking random points...

Asked by Joe Bannen on 5 Nov 2015
Latest activity Commented on by Thorsten
on 5 Nov 2015
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

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1 Answer

Answer by Stephen Cobeldick on 5 Nov 2015
Edited by Stephen Cobeldick on 5 Nov 2015
 Accepted Answer

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

  4 Comments

Show 1 older comment
Define your interval and distribution, and use these to generate some indices, exactly as I have shown.
Do you know which distribution you need?
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
Maybe you want to sort the 10 randomly picked numbers:
t=linspace(0,1);
t10 = t(sort(randperm(numel(t), 10)))

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