Having some problems with recursive function

function S = mySum(A)
S = plus(A, length(A))

function total = plus(arr, leng)
if(leng == 0)
   total = 0
else
   total = arr(leng) + plus(arr,leng - 1)
end

The above codes is used for computing the sum of the elements in an array. The problem here is that the function always returns "total = 0".

However, the function returns the correct value if i change

total = arr(leng) + plus(arr,leng - 1)

to

total = arr(leng) () plus(arr,leng - 1)

After debugging the script several times i realized some strange behaviours at "total". After plus(arr, 0) return 'total = 0'.

It will be total = arr(1) + 0, so this should be the sum of arr(1) and '0'. However, this calls plus(arr(1), 0).

Therefore, when i change :

if(leng == 0)

total = 50

Again, 'total = arr(leng) + plus(arr, leng - 1)' calls function plus(arr(leng), plus(arr, leng - 1)).

Here, 'total = arr(1) + plus(arr, 0)' calls function plus(arr(1), 50).

Can someone please explain whether 'total = arr(leng) + plus(arr,leng - 1)' calls (arr(leng), plus(arr, leng - 1)) or not and also the solution in this case.

Thanks a lot for your contribution.

Answer 1

[Dennis]

This strange behaviour originates in a unfortunate function name.

function S = mySum(A)
S = myplus(A, length(A))
function total = myplus(arr, leng)
if(leng == 0)
   total = 0
else
   total = arr(leng) + myplus(arr,leng - 1)
end

[Guillaume]

This strange behaviour originates in a unfortunate function name.

To clarify that, plus is the functional name of the + operator. By naming your function plus you effectively changed the way addition worked.

Similar function names to avoid, minus, times, sum, mean, etc.

Didn't you get a warning when you saved your file:

Warning: Function plus has the same name as a MATLAB builtin. We suggest you rename the function to avoid a potential name conflict.

[David Joseph]

Wow. Thanks alot ! I get it