mean() is giving me an error, when when I use the test code Matlab suggests

Hi,

I am unable to reproduce the code given on the help page for the mean() function, https://www.mathworks.com/help/matlab/ref/mean.html

Here is the code I'm trying to run (I have version R2018a installed)

A(:,:,1) = [2 4; -2 1];
A(:,:,2) = [9 13; -5 7];
A(:,:,3) = [4 4; 8 -3];
M1 = mean(A,[1 2])

I keep getting the error:

Error using sum

Dimension argument must be a positive integer scalar within indexing range.

Error in mean (line 116)

y = sum(x, dim, flag) ./ size(x,dim);

I'm not sure why this is happening since this is the code given by the Matlab people, so it should work. Could someone help me with this please? Thanks.

[Stephen23]

"I'm not sure why this is happening since this is the code given by the Matlab people, so it should work."

This feature was introduced in R2018b. You can search for when features were introduced by using the Relase Notes:

https://www.mathworks.com/help/matlab/release-notes.html?rntext=mean&startrelease=R2018a&endrelease=R2018b&groupby=release&sortby=descending

While the online help is useful and interesting, if you actually want to know what your installed MATLAB can do, then you easiest solution is to use the documentation of your installed MATLAB, not the online help for the current version.

[rpinto73]

Hi Stephen,

Your tone is quite condescending. It was not obvious that this feature was only introduced in 2018b, since I didn't see it indicated anywhere on the help page for the mean() function that there were new functionalities only introduced in R2018b.

It's also not clear how to only search for documentation for 2018a.

[Stephen23]

"It's also not clear how to only search for documentation for 2018a."

1. The easiest way is to simply use the installed documentation, which is always correct for whatever version you are using.
2. If you want online documentation (change to suit the version):

https://www.mathworks.com/help/releases/R2018a/matlab/ref/mean.html

[rpinto73]

Thanks for the tips.

[Jan]

I do not see any condescending tone in Stephen's useful comment.

Answer 1

[Stephan]

Hi,

if you work with R2018a you should use the documentation from R2018a instead of R2018b. Work through the correct documentation and you will have success. Try:

M1 = mean(mean(A,1),2)

Best regards

Stephan

[rpinto73]

Hi Stephan,

Thank you so much for your answer and for including the link to the R2018a documentation - I didn't realize the functionality of mean() had changed from 2018a to 2018b, and was not sure how to access that 2018a documentation that Stephen mentioned in his comment.

Thanks again,

Rebecca