Calculating the Standard Deviation

Hi,

How to read each value from a txt file for calculation of standar deviation (SD).

For example, I have my txt file with Y values (frequencies) and I want to caulate how much of variation from the mean the frequencies change. I can do it manually but for many data this would be too slow process. So, I want to automatically read and calculate the SD.

My file has jus one colum. To calculate the SD I have to calculate mean first, so would be: Mean = A/n

The variable A would be the sum of each value in my file divivded by the total number of values. Attached is the file. Then, I can calculate the SD which is

the sqr((A(1)-Mean)^2 + (A(2)-Mean)^2 + ... + (A(N)-Mean)^2/n-1).

Is there a way to do it automatic?

Thank you

[Tay]

File attached is that helps

[Stephen23]

https://web.archive.org/web/20211124063507/https://www.mathworks.com/matlabcentral/answers/822270-calculating-the-standard-deviation

Answer 1

[Star Strider]

Two options are to either calculate it directly, or use the normalize funciton —

y = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/608245/y%20axis.txt')

y = 400×1

10.5400 10.5200 10.5231 10.5138 10.5015 10.5015 10.5108 10.5046 10.5231 10.4846

ymean = mean(y)

ymean = 10.2223

stdvct = sqrt((y-ymean).^2)

stdvct = 400×1

0.3177 0.2977 0.3008 0.2916 0.2792 0.2792 0.2885 0.2823 0.3008 0.2623

[N,C,S] = normalize(y,'center','mean')

N = 400×1

0.3177 0.2977 0.3008 0.2916 0.2792 0.2792 0.2885 0.2823 0.3008 0.2623

C = 10.2223

S = 1

[Tay]

Thanks, Star.

Don't know why I have this error

Error using normalize
Too many output arguments.

Error in Untitled (line 2)
[N,C,S] = normalize(y,'center','mean');

[Tay]

y = readmatrix('y axis.txt');
[N,C,S] = normalize(y,'center','mean');

[Star Strider]

My pleasure!

‘Don't know why I have this error’

Nor do I.

I am using R2021a, as does the online application that I used to run this. If you are not, perhaps an upgrade is in order?

[Tay]

Thank you.

I calculated directed using the equation more easy than tryng to find the error xD

[Star Strider]

As always, my pleasure!