adding adjacent n elements in a matrix

if i have a matrix like A= (1 2 3 4;5 6 7 8;9 10 11 12 ; 13 14 15 16) adding three adjacent elements will look like A(i,j)+A(i,(j+1))+A(i,(j+2)) how can i do this for n adjacent elements ?

Answer 1

[Andrei Bobrov]

A= [1 2 3 4;5 6 7 8;9 10 11 12 ; 13 14 15 16];

out = conv2(A,[1 1 1],'valid')

[OLUBUKOLA ogunsola]

@Andrei Bobrov , thanks . works for addition of three adjacent numbers, how do you make this work for n adjacent numbers? thats the real headache

[Stephen23]

Pick N to suit:

 conv2(A,ones(1,N),'valid')

[OLUBUKOLA ogunsola]

Thanks