HOW CAN I CACULATE THE SUM OF HUGE LIST OF REALS WITHOUT STACK OVERFLOW .

abdelrahman · Unread post by **abdelrahman** » 21 Oct 2011 21:56

My Dear friends
I have a huge list of Reals Like [22222,35555,98989,........].
I would like to calculate the sum of all list Elements ,
when i Use non tail Recursive Procedure i got
Stack overflow Error ??
Any one Can Help me ???
thanks

abdelrahman · Unread post by **abdelrahman** » 21 Oct 2011 22:51

Code: Select all

predicates 
                               % calculate the sum of list of Reals 
    list_sum:(real* List ,real Start ,real Result)procedure (i,i,o).
 
clauses
   list_sum([],R,R).
  
   list_sum([H|T],Start,Result):-
       NewStart=H+Start,
       list_sum(T,NewStart,Result).
       
 
goal 
 list_sum(List,0,Result).

shall be so grateful for your comments .
abdelrahman

Paul Cerkez · Unread post by **Paul Cerkez** » 22 Oct 2011 1:31

the simplest way I would do this is:

Code: Select all

facts
  realtotal :(real) :=0.0.
 
predicates 
% calculate the sum of list of Reals 
list_sum:(real* List )procedure (i). 
 
clauses 
list_sum([]). 
 
list_sum([H|T]):- 
    realtotal :=H+realtotal , 
    list_sum(T). 
 
goal 
   realtotal:=0.0, % makes sure its starts at 0
   list_sum(List),
   stdio::write(toString(realtotal)).

single pass with no backtracking. would handle a list of any size with no memory issues.

abdelrahman · Unread post by **abdelrahman** » 22 Oct 2011 23:02

My Dear Paul , thank you very much for your sentences ,
but i have an explanation ,
can i use this predicate with wide scope through many classes or
hence it uses object fact , it should be used locally at the scope of current class .
forgive me I am so novice in OOP.
Need more Declaration , thanks for your interest ...
abdelrahman

Steve Lympany · Unread post by **Steve Lympany** » 23 Oct 2011 7:42

Hi,
Please let me interrupt...

I don't understand why you get a stack overflow with your code. Your code is correct. How many numbers are you adding? Maybe it is the list itself causing the problem, and not the summing. But I have made a list of 10^6 reals with no problem.

Anyway, the following adjustments to Paul's code should work. It is not very nice, but maybe it will avoid the stack overflow.

1) Make the predicate a class predicate. Declare it in the .cl file (and then it can be used anywhere in your program):

Code: Select all

predicates
    list_sum:(real* List )->real.

2) In the pro file:

Code: Select all

class facts
  realtotal :(real) :=0.0.
 
clauses
list_sum([])=real_total:-!.
 
list_sum([H|T])=0:-
    realtotal :=H+realtotal ,
    _=list_sum(T).

Try it and see.
cheers
Steve

abdelrahman · Unread post by **abdelrahman** » 23 Oct 2011 15:29

My Dear Steve ,
the code i've published here is working and not the code that produces Stack overflow ,
the one that produced stack overflow was non_tail Recursive one . i didn't write it ,
i replaced it with this new one . but i expected that i am novice and you with many other friends are professionals and can write more elegant and effective code .
the global declaration you wrote is the effective one that i am searching for it to use the predicate with wide scope through many classes ...
thank you Very much Steve ..
abdelrahman

Unread post by **Thomas Linder Puls** » 24 Oct 2011 14:56

Personally, I am not very happy about using class facts as local temporary variable of a predicate.

So I prefere your own solution.

If you insist on using a modifiable variable, then I would suggest that you use the varM class:

Code: Select all

clauses
    list_sum(L) = Sum:value :-
        Sum = varM::new(0),
        foreach V = list::getMember_nd(L) do
            Sum:value := Sum:value+V
        end foreach.

Paul Cerkez · Unread post by **Paul Cerkez** » 24 Oct 2011 15:00

very interesting Thomas, I did not know we had that capability.

I used the class facts because I did not know about the varM class.

thanks

Steve Lympany · Unread post by **Steve Lympany** » 24 Oct 2011 15:37

Hi,
I keep forgetting to use varM!!

cheers
Steve

abdelrahman · Unread post by **abdelrahman** » 25 Oct 2011 3:25

My Dear Thomas , thanks for your New Idea ,
actually by Trial , unfortunately Steve's code also produced a stack over flow ,,,
so i returned to the working Tail recursive code .
I didn't try your code yet and Because I didn't use the varM Class Before ,studying For Each , hence
your code needs me more time to understand ...
on my opinion , I think simple ideas directly using variables are much more easier when works efficiently .
Again ,
Thanks ...

Gukalov · Unread post by **Gukalov** » 25 Oct 2011 12:01

Another way: list::forAll() is the same foreach...getMember_nd loop.

Code: Select all

clauses
    list_sum(L) = Sum:value :-
        Sum = varM::new(0),
        list::forAll(L,{(V):- Sum:value := Sum:value+V}).

Paul Cerkez · Unread post by **Paul Cerkez** » 20 Nov 2011 16:24

Thomas,
is varM only in VIP 7.3 and later. I tried to use it in a 7.2 application it came back as unknown.

P.

Unread post by **Thomas Linder Puls** » 20 Nov 2011 19:17

Yes, varM was introduced in Vip7.3 together with the collection library; all requiring generic interfaces and classes (introduced in Vip 7.3)

Paul Cerkez · Unread post by **Paul Cerkez** » 20 Nov 2011 19:34

thanks Thomas,

at least now I know I am not completely crazy (although I know a few folks who might argue the fact)

HOW CAN I CACULATE THE SUM OF HUGE LIST OF REALS WITHOUT STACK OVERFLOW .

HOW CAN I CACULATE THE SUM OF HUGE LIST OF REALS WITHOUT STACK OVERFLOW .

this solution worked without stack overflow .. any comment my friends ....

My Dear paul Thank you , but can i use this with wide scope .

MY Dear Steve , thank you for your interest ...

My Dear Thomas , thanks .