MATLAB: Help with this Matrix summation

matrixsum

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!

Best Answer

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

Related Solutions

MATLAB: Summation with for loops

I’m not certain what a ‘summation graph’ is.

One of these will probably do what you want:

x = -10:10;
y = zeros(size(x));
for n=1:21
    for k=1:11
        terms(n,k) =  k.*(-x(n)).^(k-1);
    end
end
row_cumsum = cumsum(terms);
col_cumsum = cumsum(terms,2);
row_sum = sum(terms);
col_sum = sum(terms,2);
figure
plot(row_cumsum)
figure
plot(col_cumsum)
figure
plot(row_sum)
figure
plot(col_sum)

Experiment to get the result you want.

MATLAB: Summation of rows , then columns in matrix

This works:

F = [ 3 4 5 6 2 ; 4 5 2 6 6; 8 4 3 6 7 ; 5 6 3 8 5 ];
Fc = sum(F,2);
Fr = sum(F);
Sum = [Fr Fc']
Sum =
    20    19    13    26    20    20    23    28    27

Note — Row 1 of ‘F’ has an extra 2. The version here is correct., and gives the correct result.

Best Answer

Related Solutions

MATLAB: Summation with for loops

MATLAB: Summation of rows , then columns in matrix

Related Question