discuss.visual-prolog.com

Posted: **25 Jun 2015 8:36**

What are the differences between the following operators:-
- div and quot ?
- mod and rem ?

Posted: **25 Jun 2015 12:58**

The difference is in handling of negative numbers. See: Integral division.

Posted: **26 Jun 2015 7:14**

Thanks. I'm working with positive numbers and I note that div and quot have the same effect.

Posted: **26 Jun 2015 11:43**

Yes, for positive numbers there is no difference.

div has the mathematical sensible property:

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B div C = (B-C) div C - 1

I.e. the result becomes one less if you subtract the divisor from the dividend.

quot does not preserve this property: the point where the result should go from 0 to -1 it will stay once more at 0. I am not really sure when you want this behavior.

We have introduced quot/rem to maintain access to the behavior div/mod used to have.

Posted: **7 Jul 2015 12:39**

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predicates
% 2015.07.07. Modulus with real arguments and results>=0.
    realModU:(real Divided, ureal Divisor) -> ureal Modulus.
    realModR:(real Divided, real Divisor) -> ureal Modulus.
 
clauses
% 2015.07.07. Modulus with real arguments and results>=0.
    realModU(Divided,Divisor) = Divided-Divisor*floorToReal(Divided/Divisor).
    realModR(Divided,Divisor) = Divided-abs(Divisor)*floorToReal(Divided/abs(Divisor)).

Posted: **1 Aug 2015 4:13**

Corrected version

Code: Select all

predicates
% 2015.07.07. Modulus with real arguments and results>=0.
    realModP:(real Divided, positive Divisor) -> ureal Modulus. % 2015.07.19.
    realModU:(real Divided, ureal Divisor) -> ureal Modulus.
    realModR:(real Divided, real Divisor) -> ureal Modulus.
 
clauses
% 2015.07.19. Modulus with real arguments and results>=0.
    realModP(Divided,Divisor) = Divisor*CorrectedFraction :-
        Fraction=fraction(Divided/Divisor),
        if Fraction<0 then
            CorrectedFraction=1+Fraction %<=== ESSENCE OF CORRECTION
        else
            CorrectedFraction=Fraction
        end if.
 
    realModU(Divided,Divisor) =  Divisor*CorrectedFraction :-
        Fraction=fraction(Divided/Divisor),
        if Fraction<0 then
            CorrectedFraction=1+Fraction
        else
            CorrectedFraction=Fraction
        end if.
 
    realModR(Divided,Divisor) = realModU(Divided,abs(Divisor)).

The essence of the correction is the

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        if Fraction<0 then
            CorrectedFraction=1+Fraction
        else
            CorrectedFraction=Fraction
        end if.

insertion.
Example usage

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