Apply function on array

I would like to create function which will take number from the second position in array, add numbers from the first and third position in that array and write down as a second position in the output array. So the formla would be F2=A1+A2+A3 if A is our input array and F is output. It should work for unknow lenght of array and take 0 for first and last number (so for F1= 0+A1+A2). I would be very thankful for any advice how I should do it...

Answer 1

[madhan ravi]

Probably you're looking for cumsum()

doc cumsum

Answer 2

[Star Strider]

Try this:

A = randi(9, 10, 1)                                     % Create ‘A’
F = zeros(size(A));                                     % Preallocate ‘F’
F1 = filter([1 1 1], 1, A);                             % All Releases
F2 = movsum(A, [1 1]);                                  % In R2016a & Later

F(2:end-1) = F1(3:end)                                  % Desired Output
F(2:end-1) = F2(2:end-1)                                % Desired Output

Experiment to get the result you want