counting n subsequent element of an array

say i have an array a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

is there a easy way to add say n=3 elements at a time and form another array b. that is elements of b will be as follows:

 b = [1+2+3, 2+3+4, 3+4+5, 4+5+6, 5+6+7,6+7+8,7+8+9, 8+9+10];

Answer 1

[Matt J]

 b = conv(a,[1 1 1],'valid')

Answer 2

[Azzi Abdelmalek]

a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
n=3
b=arrayfun(@(x) sum(a(x:x+n-1)),1:numel(a)-n+1)