# How to multiple set of normally distributed data?

조회 수: 1(최근 30일)
Kuhinur Shukurjonov 2021년 7월 22일
댓글: Kuhinur Shukurjonov 2021년 7월 23일
I developed the following code to find the multiplication of 2 sets of random variables:
rng(0, 'twister');
b2=1.00; % average
a2=0.50; % standard deviation
x2=a2.*randn(10000000,1)+b2;
rng(0, 'twister');
b1=0.23; %average
a1=0.12; %standard deviation
x1=a1.*randn(10000000,1)+b1;
x3=x2.*x1;
m1=mean(x3)
s1=std(x3)
c1=s1/m1;
Now I want to modify code by using "for" loop(target: to find x3=x2.*x1 for arrays of a1,a2,b1, b2)
rng(0, 'twister');
b2=[1.00];
a2=[0.50];
b1=[0.23];
a1=[0.12];
for i=1:length(b2)
x2=a2(i).*randn(10000000,1)+b2(i);
x1=a1(i).*randn(10000000,1)+b1(i);
x3(:,i)=x2.*x1;
m1(i)=mean(x3(:,i))
s1(i)=std(x3(:,i))
c1(i)=s1(i)/m1(i);
end
However, the resluts of "for" loop is not coincede with the results of previous method.
How can I solve this problem?

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### 채택된 답변

dpb 2021년 7월 22일
You rest the RNG before each of the two sets in first code segment but only at the beginning of the loop in the second so the two x1 sequences aren't the same.
No idea what the purpose of this might be for, but either
rng(0, 'twister');
b2=1.00; % average
a2=0.50; % standard deviation
x2=a2.*randn(10000000,1)+b2;
%rng(0, 'twister');
b1=0.23; %average
a1=0.12; %standard deviation
x1=a1.*randn(10000000,1)+b1;
x3=x2.*x1;
m1=mean(x3)
s1=std(x3)
c1=s1/m1;
without changing the second code segment or
b2=[1.00];
a2=[0.50];
b1=[0.23];
a1=[0.12];
for i=1:length(b2)
rng(0, 'twister');
x2=a2(i).*randn(10000000,1)+b2(i);
rng(0, 'twister');
x1=a1(i).*randn(10000000,1)+b1(i);
x3(:,i)=x2.*x1;
m1(i)=mean(x3(:,i))
s1(i)=std(x3(:,i))
c1(i)=s1(i)/m1(i);
end
leaving the first unchanged will produce the same overall sequence of randn()
It makes no sense to me to do either in isolation here; I suppose there might be some situation this mimics that it would be a reason for one or the other cases this simulates.
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Kuhinur Shukurjonov 2021년 7월 23일
Great. Thank you I got what I wanted. The code works well.

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R2019b

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