How to add multiple values from column together

Lets assume I have a vector a with n values

a = rand(n,1) % values

and I priovide another vector b containing some row indices of the vector above

b = [1 3 8 9 11 15 ..] % indices from vector a

How can I add the values from these rows together without using a loop?

Answer 1

[Daniel Catton]

n = 10
a = rand(n,1);
b = sum(a);

[link]

Hey, I do not want to add all values from, but only the values from the indices I provided in a second vector

[Daniel Catton]

Oh I get you now, my bad. I thing you're going to struggle without using a loop. I can't think of a way without just coding the way a loop works. i.e:

a = rand(n,1); % values

b = [1 3 8 9 11 15 ..] % indices from vector a

a(b(1))+a(b(2))+a(b(3))+...