File: SUMMIN.PS of Tape: Various/Decus/decus-3

(Source file text) 

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PROGRAM SUMMING(OUTPUT);

 (* COMPUTE 1 - 1/2 + 1/3-...+1/9999 - 1/10000 , 4 WAYS.
     1) LEFT TO RIGHT, IN SUCCESSION
     2) LEFT TO RIGHT, ALL POS AND NEG TERMS, THEN SUBTRACT
     3) RIGHT TO LEFT IN SUCCESSION
     4) RIGHT TO LEFT, ALL POS AND NEG TERMS, THEN SUBTRACT*)

VAR S1,S2P,S2N,S3,S4P,S4N,LRP,LRN,RLP,RLN  : REAL;
I  : INTEGER;
BEGIN S1 := 0; S2P := 0;  S2N := 0; S3 := 0; S4P := 0; S4N := 0;
   FOR I := 1 TO 5000 DO
   BEGIN
      LRP := 1/(2*I-1); (* POS TERMS, LEFT TO RIGHT *)
      LRN := 1/(2*I); (* NEG TERMS, LEFT TO RIGHT *)
      RLP := 1/(10001-2*I);  (* POS TERMS, RIGHT TO LEFT *)
      RLN := 1/(10002-2*I);  (* NEG TERMS, RIGHT TO LEFT *)
      S1 := S1 + LRP - LRN;
      S2P := S2P + LRP; S2N := S2N + LRN;
      S3 := S3 + RLP - RLN;
      S4P := S4P + RLP; S4N := S4N + RLN
   END;
   WRITELN(S1,S2P-S2N);
   WRITELN(S3,S4P-S4N)
END.

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