topic Re: summing a series in SAS Programming

summing a series

AmirSari — Mon, 09 Mar 2020 08:56:17 GMT

Dear SAS Experts,

I am trying to sum a series using a do loop but I cannot seem to figure out how to do that as I am getting errors in all my attempts.

here is what tried and failed:

do while(n<addyrs);
do t = 6 to (n+6);
   sum = 0;
      sum = EMLP/((1+K)**t);
   end;
  end;

when I run this code I get the following error:

ERROR: Invalid DO loop control information, either the INITIAL or TO expression

is missing or the BY expression is missing, zero, or invalid.

Thanks!

Re: summing a series

gamotte — Mon, 09 Mar 2020 09:29:33 GMT

Hello,

Can you show a complete runnable code ?

Here, you will have an infinite loop as n is not modified inside the loop.

The error message can result from variables in the do statements having missing values.

Re: summing a series

gamotte — Mon, 09 Mar 2020 09:35:37 GMT

Also, in your code, sum is reinitialized at each step.

I think you meant :

sum=0; n=0;
do while(n<addyrs);
do t = 6 to (n+6);
      sum + EMLP/((1+K)**t);
   end;
   n+1;
  end;

Edit : added an n increment to avoid an infinite loop but it might not be what you need.

Re: summing a series

FreelanceReinh — Mon, 09 Mar 2020 10:10:34 GMT

Hello @AmirSari,

Simplify your code and use a single DO loop:

data want(drop=t);
K=0.02; EMLP=17; Addyrs=42; /* replace with your values */
do t=6 to 6+Addyrs;
  sum + EMLP/((1+K)**t);
end;
run;

Or use the formula for the geometric sum, then you don't need a loop at all:

data want(drop=q);
K=0.02; EMLP=17; Addyrs=42; /* replace with your values */
q=1/(1+K);
sum=EMLP*q**6*(1-q**(Addyrs+1))/(1-q);
run;

Re: summing a series

ballardw — Mon, 09 Mar 2020 19:18:04 GMT

It is almost never a waste of time to provide a small example data set, especially in the form of data step code, of the start and the desired result.

Re: summing a series

AmirSari — Mon, 09 Mar 2020 19:56:35 GMT

Thanks everybody for your replies! I will provide an example next time!