Random number generate in an interval

Question

Guilherme Lopes de Campos 2023-9-14

1
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https://ww2.mathworks.cn/matlabcentral/answers/2021091-random-number-generate-in-an-interval

评论： Walter Roberson 2023-9-22

在 MATLAB Online 中打开

Hi community,

I would like to generate random number in the follow distribuition: Normal, Gamma and Weibull.

Amount of data required: 5000 numbers at interval [a,b]

At the example, it was used the follow code:

A = linspace(0,1,5000)
sr = size(A)
b = normrnd(27.5,15.73,sr)
plot(b)

Its works, however, the valid interval to generate was [1,54]

Can us help me, please?

Yours faithfully

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Walter Roberson 2023-9-14

在 MATLAB Online 中打开

(27.5 - 1) / 15.73
ans = 1.6847
(54 - 27.5) / 15.73
ans = 1.6847

Less than 2 standard distributions -- the excluded area is non-trivial, and will make a significant difference in normality.

A = linspace(0,1,5000)
A = 1×5000
         0    0.0002    0.0004    0.0006    0.0008    0.0010    0.0012    0.0014    0.0016    0.0018    0.0020    0.0022    0.0024    0.0026    0.0028    0.0030    0.0032    0.0034    0.0036    0.0038    0.0040    0.0042    0.0044    0.0046    0.0048    0.0050    0.0052    0.0054    0.0056    0.0058
sr = size(A)
sr = 1×2
           1        5000
b = normrnd(27.5,15.73,sr);
[min(b), max(b)]
ans = 1×2
  -45.4716   84.9146
pd = fitdist(b.','Normal')
pd = 
  NormalDistribution

  Normal distribution
       mu = 27.3657   [26.9338, 27.7975]
    sigma = 15.5758   [15.2764, 15.8872]
btrunc = max(1, min(b, 54));
[min(btrunc), max(btrunc)]
ans = 1×2
     1    54
pd2 = fitdist(btrunc .', 'Normal')
pd2 = 
  NormalDistribution

  Normal distribution
       mu =  27.383   [26.9857, 27.7802]
    sigma = 14.3283   [14.0529, 14.6148]

The standard distribution of the truncated version is notably different.

Walter Roberson 2023-9-14

在 MATLAB Online 中打开

Right, different interpretations of what "clipping" means in the context.

format long g
b = normrnd(27.5,15.73,[1 500000]);
out_of_range = (b < 1) | (b > 54);
mean(out_of_range) * 100
ans = 
                     9.195

so over 9% of the samples are outside of the target range

Walter Roberson 2023-9-22

@Guilherme Lopes de Campos comments to @Bruno Luong

It works! Thank you very much

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Answer 1

the cyclist 2023-9-14

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https://ww2.mathworks.cn/matlabcentral/answers/2021091-random-number-generate-in-an-interval#answer_1310421

编辑：the cyclist 2023-9-14

A normal distribution, by definition, has support from negative infinity to positive infinity. You cannot have both a normal distribution and a finite range.

You can use the truncate function to create a truncated normal distribution object, and draw values from that. (See the second example on that page.) Is that what you want?