sum

Sum of elements in an array

Usages

s = sum(A)

• If A is a scalar, s is equal to A.
• If A is a vector, s is the sum of all elements along the longer dimension of A.
• Otherwise, each element of s is the sum of all elements of the corresponding vector of A along the first non-singleton dimension.
• If A is empty, it returns an empty array.

s = sum(A, k)

• This is the same as s = sum(A), except that each element of s corresponds to a vector of A along its k-th dimension.
• If the k-th dimension has zero length, then it returns an empty array.

💡 When adding up numbers by sum, if any one of them is NaN, the result will be NaN.

Examples

• Finding the sum of a 3D array along the 3rd dimension.

Input

a = [1 2 3; 1 2 3; 1 2 3];
% Creating a 3D array by repeating a matrix along the 3rd dimension.
b = repmat(a, [1, 1, 3])
% The sum along the 3rd dimension.
sum(b, 3)

Output

b(:, :, 1) = 
 1.0000   2.0000   3.0000
 1.0000   2.0000   3.0000
 1.0000   2.0000   3.0000

b(:, :, 2) = 
 1.0000   2.0000   3.0000
 1.0000   2.0000   3.0000
 1.0000   2.0000   3.0000

b(:, :, 3) = 
 1.0000   2.0000   3.0000
 1.0000   2.0000   3.0000
 1.0000   2.0000   3.0000

ans = 
 3.0000   6.0000   9.0000
 3.0000   6.0000   9.0000
 3.0000   6.0000   9.0000