how to add to previous value in matlab

Suppose i have a matrix

a=[1 2 3 4 5]

I want to add a number such as 2 to the first number in matrix a. so its like

a1=[3 2 3 4 5]

then i want to do a loop or any other function to keep on adding to the previous value from the second number, so it becomes

a2=[3 5 8 12 17]

what code should i write to make this?

Answer 1

[Star Strider]

Adding a value to the first element simply requires:

a=[1 2 3 4 5]
a(1) = a(1) + 2

The ‘... then I want ...’ part does not require a loop, however it does require the cumsum function:

a = cumsum(a)

producing collectively:

a =
     1     2     3     4     5

a =
     3     2     3     4     5

a =
     3     5     8    12    17

as requested.