Help with this Matrix summation?

Hi guys,

I am having trouble with matrix summation.

For example, let's say Y = [5 6 7; 17 18 19]. If I do sum(Y), ans = [22 24 26]. Good, this is what I want.

But when Y = [17 18 19], the sum(Y) = 54.

How can I make it so that no matter what it takes the sum of, the answer will always output a row of sums of the columns of Y? I need this because for my function, I don't know what matrix values I will get, but I will always need an output that is a row vector.

Ex. Y = [17 18 19]. ans = [17 18 19].

Thank you!

Answer 1

[Star Strider]

The second argument to sum is the dimension to sum across.

Example —

Y = [5 6 7; 17 18 19];
col_sum = sum(Y,1)
row_sum = sum(Y,2)

col_sum =
    22    24    26

row_sum =
    18
    54

[Jihun Sung]

Ah, so simple!

Thank you so much.

[Star Strider]

As always my pleasure!

The ‘dimension’ conventions can be a bit confusing until you get used to them.