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Finding random normally distributed number above zero

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Tishan Anantharajah
评论： Paul 2023-4-15
I am currently using randn to produce a normally distributed number however would like to only take the positive side for the normally distributed curve. How could this be done? Would I have to use a loop?

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回答（3 个）

Torsten
Torsten 2023-4-15
编辑：Torsten 2023-4-15
Ran in:
Maybe taking abs(randn()) will give you something useful. It's the folded normal distribution (which in this case equals the truncated normal distribution):
https://en.wikipedia.org/wiki/Folded_normal_distribution
https://en.wikipedia.org/wiki/Truncated_normal_distribution
n = 100000;
y = abs(randn(n,1));
hold on
histogram(y,'Normalization','pdf')
fun = @(x)sqrt(2/pi)*exp(-x.^2/2);
x = 0:0.01:4;
plot(x,fun(x))
hold off
  2 个评论
Paul
Paul 2023-4-15
Ran in:
Can also use the HalfNormalDistribution if it's needed to do more than just generate random numbers.
n = 100000;
y = abs(randn(n,1));
hold on
histogram(y,'Normalization','pdf')
x = 0:0.01:4;
plot(x,pdf('HalfNormal',x,0,1))
hold off

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Star Strider
Star Strider 2023-4-15
The truncate function is another option.
Image Analyst
Image Analyst 2023-4-15
You could just throw away any less than zero:
r = stDev * randn(100000, 1) + desiredMeanValue;
r(r<=0) = [];
% Or equivalently
r = r(r > 0);
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