Finding sum of a Matrix

We may use a single colon as an index into a matrix selects all the elements of the array and arranges them (in column order) into a single column vector, Like :

Example

>> A = [1,2,3; 4,5,6; 7,8,9]

A =

     1     2     3
     4     5     6
     7     8     9

>> A(:)

ans =

     1
     4
     7
     2
     5
     8
     3
     6
     9

Same colon used to find the sum of whole matrix as :

>> sum(A(:))

ans =

    45

We may find sum of Individual columns as :

>> A = [1,2,3; 4,5,6; 7,8,9]

A =

     1     2     3
     4     5     6
     7     8     9

>> sum(A)

ans =

    12    15    18