Finding random normally distributed number above zero
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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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Answers (3)
Torsten
on 15 Apr 2023
Edited: Torsten
on 15 Apr 2023
Maybe taking abs(randn()) will give you something useful. It's the folded normal distribution (which in this case equals the 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
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Paul
on 15 Apr 2023
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
Image Analyst
on 15 Apr 2023
You could just throw away any less than zero:
r = stDev * randn(100000, 1) + desiredMeanValue;
r(r<=0) = [];
% Or equivalently
r = r(r > 0);
To learn other fundamental concepts, invest 2 hours of your time here:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1357408/image.png)
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