How to calculate mean and variance?

Question

SHRIVATHSA S. 2017-1-19

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回答： Nikos Lambadakis 2022-4-1

Greetings. I have generated a vector of 10,000 complex samples. I want to calculate the Mean and Variance of the samples. How can I do it without using the built-in functions _ mean()_ and * var()* ? and how do I do that in a loop? Please help.

Thank you

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Ana Soph 2020-5-6

How can convert to 1 minute to 10 minutes, a wind directio data ? please, i have a matrix fo 1440x31

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Answer 1

Jorge Mario Guerra González 2017-1-19

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编辑：Jorge Mario Guerra González 2017-1-19

在 MATLAB Online 中打开

Since you want to do it without using the functions, just do:

    A=rand(1000,1); %your array
sum1=0;
for i=1:length(A)
  sum1=sum1+A(i);
end
M=sum1/length(A); %the mean
sum2=0;
for i=1:length(A)
    sum2=sum2+ (A(i)-M)^2;
end
V=sum2/length(A); %Varaince

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SHRIVATHSA S. 2017-1-19

Thank you @Jorge Guerra for the answer. It was really helpful

Jorge Mario Guerra González 2017-1-19

编辑：Jorge Mario Guerra González 2017-1-19

@Stephen Cobeldick absolutely agree, that was just a fast script I wrote to show the proccedure. I edited the answer

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Answer 2

Walter Roberson 2017-1-19

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Mean is the average -- the sum divided by the number of entries.

Variance is the sum of the squares of (the values minus the mean), then take the square root and divided by the number of samples

You can vectorize the calculation using sum().

To use a for loop to calculate sums, initialize a running total to 0, and then each iteration of the loop, add the current value to the running total.

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Jurgen 2017-12-19

This answer contradicts the variance formula on the MATLAB website (no square root). Oh and wikipedia disagrees. The MATLAB variance assumes a uniform probability distribution. A very important assumption.

John D'Errico 2020-7-24

@ Jurgen - you make no sense in some of what you said, although you are correct about the square root being incorrect in this answer. Variance has no square root in it.

A variance is something you can compute from the data, or for a population, but there is no assumption about the underlying distribution, nor is there any need to make such an assumption.

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Answer 3

Olayemi Akinsanya 2017-9-16

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编辑：Olayemi Akinsanya 2017-9-16

P=[10:2:70]

i wrote a script for variance, it gives me a value of 320. when i check with var(P), it gives me a value of 330.6667. can someone advice what i did wrong.