Unexpected results with Clojure core.logic (using CLP/FD)

Question

I am trying to understand why the following product-pluso function is returning unexpected results. Did I find a bug or am I misunderstanding how this works? I am using core.logic with CLP/FD. I am still learning, so I could just be doing it wrong. The function should take two factors, a number, and a sum. The sum should be the product of the factors plus the number. It works great, unless both of the factors are fresh. Then I get strange results. This is happening with core.logic v0.8.2.

(ns strang-result
  (:refer-clojure :exclude [==])
  (:use
    clojure.test
    [clojure.core.logic :exclude [is]])
  (:require
    [clojure.core.logic.fd :as fd]))

(defn product-pluso [factor1 factor2 number sum]
  (fd/eq (= sum (+ number (* factor1 factor2)))))

(run* [x y]
  (fd/in x y (fd/interval 1 38))
  (product-pluso x y 2 40))

;=> ([1 38] [2 19] [3 13] [4 10] [5 8] [6 7] [7 6] [8 5] [9 5] [10 4] [11 4] 
;    [12 4] [13 3] [14 3] [15 3] [16 3] [17 3] [18 3] [19 2] [38 1])

Just to clarify, each [x y] pair should multiply to 38 (38 + 2 = 40), but many do not. — Steve Sloan
– Steve Sloan, Commented Mar 28, 2013 at 3:07

dnolen · Accepted Answer · 2013-03-29 03:46:34Z

2

This just appears to be a bug. Something strange is happening with fd/+ constraint that is not being checked. I'm one of the lead developers, I've filed a ticket for this:

http://dev.clojure.org/jira/browse/LOGIC-126

UPDATE: Please try 0.8.3, the issue has been resolved there and you should see only 4 results. Thanks for the report.

edited Mar 29, 2013 at 3:46

answered Mar 28, 2013 at 17:09

dnolen

18.6k4 gold badges65 silver badges71 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

dnolen Over a year ago

@SteveSloan it's a good catch and I'm pretty surprised it hasn't shown up before. Will try to look into it over the weekend and push out 0.8.3 with the fix.

Ankur · Accepted Answer · 2013-03-28 05:25:35Z

0

You can solve the issue using project, without project it seems to somehow ORing the constrains rather then ANDing them.

(defn product-pluso [factor1 factor2 number sum]
  (fresh [product]
         (fd/+ product number sum)
         (project [product]
                  (fd/* factor1 factor2 product))))

answered Mar 28, 2013 at 5:25

Ankur

33.7k2 gold badges50 silver badges73 bronze badges

Collectives™ on Stack Overflow

Unexpected results with Clojure core.logic (using CLP/FD)

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related