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ramsri
Active User
Joined: 18 Oct 2008
Posts: 380
Location: India
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Hi,
was working out this example given in Zeller's congruence page in wikipedia but don't understand it. 
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However, for March 1, 2000, the date is treated as the 3rd month of 2000, so the values become
q = 1
m = 3
K = 0
J = 20
so the formula evaluates as (1 + 10 + 0 + 0 + 5 − 40) mod 7 = −24 mod 7 = 4 = Wednesday
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24 mod 7 produces 3 remainder but how and why it is calculated to 4 and becomes Wednesday 
How to write code in COBOL or Easytrieve to achieve "something mod something"
Please help. Thanks. |
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enrico-sorichetti
Superior Member
Joined: 14 Mar 2007
Posts: 10873
Location: italy
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did You care to scroll down a few line and NOTICE
the difference between the mathematical definition of MODULO
the quirks of some software implementations
and the workaround?
if You had You would not have asked the question
as far as COBOL is concerned no need to write anything
search the forum for may posts on integer of date
for example
here
www.ibmmainframes.com/viewtopic.php?t=49988&highlight=integerofdate
and here a simple REXX snippet to show what is going on
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say "*** remainder about REXX integer division and modulo operators"
integer division 7 % 4 " 7 % 4
say "reminder 7 // 4 " 7 // 4
say ""
q = 1 ;
say "q = " q
m = 3 ;
say "m = " m
K = 00;
say "K = " K
J = 20;
say "J = " J
v1 = 13 * ( m + 1 ) % 5
say "v1 = " v1
v2 = K
say "v2 = " v2
v3 = K % 4
say "v3 = " v3
v4 = J % 4
say "v4 = " v4
h0 = q + v1 + v2 + v3 + v4 + 5*J
say "h0 = " h0
h = h0 // 7
say "h = " h
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to get
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*** remainder about REXX integer division and modulo operators
integer division 7 % 4 1
reminder 7 // 4 3
q = 1
m = 3
K = 00
J = 20
v1 = 10
v2 = 00
v3 = 0
v4 = 5
h0 = 116
h = 4
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Robert Sample
Global Moderator
Joined: 06 Jun 2008
Posts: 8696
Location: Dubuque, Iowa, USA
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| Quote: |
so the formula evaluates as (1 + 10 + 0 + 0 + 5 − 40) mod 7 = −24 mod 7 = 4 = Wednesday
24 mod 7 produces 3 remainder but how and why it is calculated to 4 and becomes Wednesda |
Details are INCREDIBLY significant in IT (and in mathematics). Yes, 24 mod 7 is 3 -- but NEGATIVE 24 mod 7 is 4. This is based upon the standard definition of modular arithmetic n=pq + r where n is -24, q is 7 so p must be -4 and r becomes 4.
COBOL supports use of REMAINDER so modular arithmetic is actually very simple in COBOL. If you don't know about REMAINDER, there's a link to IBM Manuals at the top of the page and the Enterprise COBOL Language Reference manual would be the one to start reading in. |
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Bill Woodger
Moderator Emeritus
Joined: 09 Mar 2011
Posts: 7309
Location: Inside the Matrix
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Ramsri,
Is this somehow to do with your SyncSort question? If so, why didn't you answer all the questions asked of you there so you'd not need all this stuff? If you are proceeding with Cobol, re-read what enrico mentioned about integer-of-date and associated LE callable functions. |
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ramsri
Active User
Joined: 18 Oct 2008
Posts: 380
Location: India
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Hi Enrico, Robert, Bill......thanks a lot. Yes....It is related to my SORT question which I thought to workout in COBOL or Easytrieve (beginner) !
Thanks. |
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ramsri
Active User
Joined: 18 Oct 2008
Posts: 380
Location: India
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Hi,
Please help me why I get wrong answer with Gaussian's algorithm !! For date 13th Feb 2016 I should get Saturday but it shows Friday.
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********************************* Top of Data **********************************
IDENTIFICATION DIVISION.
PROGRAM-ID. PGM00001.
ENVIRONMENT DIVISION.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-DATE.
05 WS-CC PIC 9(02).
05 WS-YY PIC 9(02).
05 WS-MM PIC 9(02).
05 WS-DD PIC 9(02).
01 WS-INT-YY PIC 9(03).
01 WS-INT-MM PIC 9(03).
01 WS-DOW1 PIC 9(03).
01 WS-DOW2 PIC 9(01).
01 WS-SHIFT-MONTH PIC 9(02) VALUE ZERO.
88 WS-MAR-CODE VALUE 01.
88 WS-APR-CODE VALUE 02.
88 WS-MAY-CODE VALUE 03.
88 WS-JUN-CODE VALUE 04.
88 WS-JUL-CODE VALUE 05.
88 WS-AUG-CODE VALUE 06.
88 WS-SEP-CODE VALUE 07.
88 WS-OCT-CODE VALUE 08.
88 WS-NOV-CODE VALUE 09.
88 WS-DEC-CODE VALUE 10.
88 WS-JAN-CODE VALUE 11.
88 WS-FEB-CODE VALUE 12.
01 WS-DAY-OF-WEEK PIC 9(01) VALUE ZERO.
88 WS-SUN-CODE VALUE 0.
88 WS-MON-CODE VALUE 1.
88 WS-TUE-CODE VALUE 2.
88 WS-WED-CODE VALUE 3.
88 WS-THU-CODE VALUE 4.
88 WS-FRI-CODE VALUE 5.
88 WS-SAT-CODE VALUE 6.
PROCEDURE DIVISION.
PERFORM 01-MAIN-PARA.
STOP RUN.
01-MAIN-PARA.
ACCEPT WS-DATE.
IF WS-DATE IS NUMERIC
PERFORM 02-CALC-PARA
ELSE
CONTINUE
END-IF.
02-CALC-PARA.
EVALUATE WS-MM
WHEN 01 SET WS-JAN-CODE TO TRUE
WHEN 02 SET WS-FEB-CODE TO TRUE
WHEN 03 SET WS-MAR-CODE TO TRUE
WHEN 04 SET WS-APR-CODE TO TRUE
WHEN 05 SET WS-MAY-CODE TO TRUE
WHEN 06 SET WS-JUN-CODE TO TRUE
WHEN 07 SET WS-JUL-CODE TO TRUE
WHEN 08 SET WS-AUG-CODE TO TRUE
WHEN 09 SET WS-SEP-CODE TO TRUE
WHEN 10 SET WS-OCT-CODE TO TRUE
WHEN 11 SET WS-NOV-CODE TO TRUE
WHEN 12 SET WS-DEC-CODE TO TRUE
END-EVALUATE.
IF WS-JAN-CODE OR WS-FEB-CODE
COMPUTE WS-INT-YY = WS-YY - 1
ELSE
MOVE WS-YY TO WS-INT-YY
END-IF.
DISPLAY 'MONTH ' WS-SHIFT-MONTH
COMPUTE WS-INT-MM = ((2.6 * WS-SHIFT-MONTH) - 0.2).
DISPLAY 'INT MONTH ' WS-INT-MM
COMPUTE WS-DOW1 = (WS-DD + WS-INT-MM + WS-INT-YY +
(WS-INT-YY / 4) + (WS-CC / 4) - (2 * WS-CC))
DISPLAY 'INT RESULT ' WS-DOW1
COMPUTE WS-DOW2 = FUNCTION MOD (WS-DOW1, 7).
DISPLAY 'RESULT ' WS-DOW2
EVALUATE WS-DOW2
WHEN 0 DISPLAY 'DAY OF WEEK FOR GIVEN DATE: SUNDAY'
WHEN 1 DISPLAY 'DAY OF WEEK FOR GIVEN DATE: MONDAY'
WHEN 2 DISPLAY 'DAY OF WEEK FOR GIVEN DATE: TUESDAY'
WHEN 3 DISPLAY 'DAY OF WEEK FOR GIVEN DATE: WEDNESDAY'
WHEN 4 DISPLAY 'DAY OF WEEK FOR GIVEN DATE: THURSDAY'
WHEN 5 DISPLAY 'DAY OF WEEK FOR GIVEN DATE: FRIDAY'
WHEN 6 DISPLAY 'DAY OF WEEK FOR GIVEN DATE: SATURDAY'
END-EVALUATE.
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Output:
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DAY OF WEEK FOR GIVEN DATE: FRIDAY
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Thanks. |
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enrico-sorichetti
Superior Member
Joined: 14 Mar 2007
Posts: 10873
Location: italy
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| Do all the other dates come out right ? |
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ramsri
Active User
Joined: 18 Oct 2008
Posts: 380
Location: India
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Enrico,
These are the dates I tried and its results:
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20000301 = THURSDAY (WRONG)
20040305 = TUESDAY (WRONG)
19711202 = THURSDAY (RIGHT)
20160213 = SATURDAY (RIGHT)
20121212 = WEDNESDAY (RIGHT)
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Thanks. |
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Bill Woodger
Moderator Emeritus
Joined: 09 Mar 2011
Posts: 7309
Location: Inside the Matrix
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| Ramsri, third and last time. I'll repeat the question. What do you want to do when the "should be Sunday" date is not a Sunday AND, on the same record, the "should be Monday" date is not a Monday? |
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Robert Sample
Global Moderator
Joined: 06 Jun 2008
Posts: 8696
Location: Dubuque, Iowa, USA
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Ramsri, I think the basic problem is you do not pay attention to details. From your earlier post:
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| Please help me why I get wrong answer with Gaussian's algorithm !! For date 13th Feb 2016 I should get Saturday but it shows Friday. |
and now you post the EXACT OPPOSITE:
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20000301 = THURSDAY (WRONG)
20040305 = TUESDAY (WRONG)
19711202 = THURSDAY (RIGHT)
20160213 = SATURDAY (RIGHT)
20121212 = WEDNESDAY (RIGHT) |
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ramsri
Active User
Joined: 18 Oct 2008
Posts: 380
Location: India
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Robert, it was my mistake.....I realized it and posted correct results.
Thanks.  |
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Robert Sample
Global Moderator
Joined: 06 Jun 2008
Posts: 8696
Location: Dubuque, Iowa, USA
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So far you've shown that you do not understand the difference between a negative 24 and a positive 24, and that you post things without reviewing them to be sure they are accurate.
Furthermore, your code makes no provision for handling the negative values that can result from the equation so I suspect your 'error" results are because you have not implemented the algorithm fully and completely. When I changed your code to allow for negative values in the MOD function, the days of the week came out correctly -- even for your "error" values. |
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ramsri
Active User
Joined: 18 Oct 2008
Posts: 380
Location: India
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Robert, implementing algorithm.......certainly confused. may I please know where do I change my code to handle negative values and how
Thanks. |
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Robert Sample
Global Moderator
Joined: 06 Jun 2008
Posts: 8696
Location: Dubuque, Iowa, USA
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| Code: |
| 01 WS-DOW1 PIC 9(03). |
must be
| Code: |
| 01 WS-DOW1 PIC S9(03). |
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Robert Sample
Global Moderator
Joined: 06 Jun 2008
Posts: 8696
Location: Dubuque, Iowa, USA
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| Based upon the posts you've made and the questions you've asked, ramsri, you need to move to Beginner's and Students Forum instead of this one as it is more suited to your skill level and questions. |
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ramsri
Active User
Joined: 18 Oct 2008
Posts: 380
Location: India
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Thank you.......got the results  |
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