MATLAB: How to sum only the positive elements in a vector using an If-Statement

homeworkif statement

How do you only sum the positive elements in a vector using an if statement?

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You can do that without if

let's say d is your array of positive and negative numbers. You want to sum only the positive ones then just do this:

sum(d(d>0))

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MATLAB: How to write a summation code when the k is not equal to j

yang-En, haven't heard from you. If the vectorized approach above is to confusing to you then try this simple and intuitive for loop. It basically uses the "continue" command to skip interations where j = k.

numPoints = 3; % Whatever...



lambda = randi(9, 1, numPoints) % Whatever...
f = randi(9, 1, numPoints) % Whatever...
h = randi(9, 1, numPoints) % Whatever...
K = length(lambda)
outerSum = 0;
for k = 1 : K
	innerSum = 0;
	% Do the inner sum over j with j not equal to k
	for j = 1 : length(h)
		if j == k
			continue; % Skip this iteration
		end
		innerSum = innerSum + h(j) * f(k);
	end
	outerSum = outerSum + lambda(k) * innerSum;
end
outerSum % Spew out to the command window so we can see what it is.

MATLAB: Create a function to…

It's not bad actually. The lines

 positive=positive
 negative-negative

are useless, and you want to create vectors of sums, not scalars. So one mistake is that you don't index variables positive and negative with the row index. To make it more efficient, you could even prealloc these variables: change

 positive=0;
 negative=0;

for

 positive = zeros(size(x, 1));
 negative = zeros(size(x, 1));

Another mistake is that k and j should go from 1 to the number of rows and columns of x. You can obtain them using function SIZE.

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MATLAB: How to write a summation code when the k is not equal to j

MATLAB: Create a function to…

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