Delete - Variance vs standard deviation when using var() and std() with decimal values from CSV file?

Question

CW 2019-11-22

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/492629-delete-variance-vs-standard-deviation-when-using-var-and-std-with-decimal-values-from-csv-file

编辑： CW 2019-11-22

采纳的回答： Philippe Lebel

2019-11-21_Empirical_Experiment_2.0_2.0_3.csv

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Hello all!

I am getting a strange error in Matlab where the variance is smaller than the standard deviation when using var() and std(), despite the fact that I am working with nW of optical power. (This is correct - the standard deviation is the square root of the variance.) The code I am using is as follows:

[D,S] = xlsread('2019-11-21_Empirical_Experiment_2.0_2.0_3.csv');
Vars = strsplit(S{15},';');
for k = 16:size(S,1)
    DataC = strsplit(S{k},';');
    pwr_2_2(k-15,:) = str2double(DataC{4});
end
mpwr_2_2=mean(pwr_2_2)
vpwr_2_2=var(pwr_2_2)
spwr_2_2=std(pwr_2_2)

The csv file is attached. I am at a loss for how to exactly diagnose this issue and I welcome any advice that you can give. I thought that the method for importing the data from the csv (thanks to some help from Matlab Answers!) was working well, but maybe the issue is rooted in the data import? Thanks in advance, and let me know if there are any questions!