What does mean(s(:)) do and the reason for using " : " for mean of a square matrix?

The working of the below mentioned and the reason for using " : " avg = mean(s(:));

Answer 1

[John D'Errico]

Well, what does mean do, when applied to a matrix? TRY IT!!!!!!!!! You will learn by trying things.

magic(3)
ans =
   8     1     6
   3     5     7
   4     9     2
>> mean(magic(3))
ans =
   5     5     5
>> mean(magic(3),2)
ans =
   5
   5
   5

So when you apply mean to a MATRIX, it finds the mean across rows, or down columns.

When you apply mean to a vector, it finds the mean of the vector elements.

mean(1:10)
ans =
          5.5

So how can you find the mean of an entire matrix?

Can you convert a matrix to a vector? If so, then you can just use mean.

What does s(:) do? It converts a matrix to a column vector. Therefore, you should now know what mean(s:)) does, and why it works.

When you don't understand some code in MATLAB, take it apart, one level at a time. Think what each part does. And if you don't know how something works, EXPERIMENT!

[SRAVAN KUMAR REDDY METTUPALLI]

Thanks, john ! Really good explanation

Answer 2

[Adam]

(:) reshapes the array to a column vector, as described in

doc colon

This is done when taking the mean of a 2d image as a simple way to avoid having to do

mean( mean( s ) )

In the case of mean and some other functions there is a special builtin function

doc mean2

but I always use the colon notation personally.

[SRAVAN KUMAR REDDY METTUPALLI]

Thanks, Adam!