From: peder@klingenberg.no (Peder O. Klingenberg)
To: 25255@debbugs.gnu.org
Subject: bug#25255: Emacs calculator evalutes lcm to a negative number
Date: Sun, 05 Feb 2017 11:28:17 +0100 [thread overview]
Message-ID: <m1efzdylry.fsf@klingenberg.no> (raw)
In-Reply-To: <112161482489139@web25j.yandex.ru> (Bug Poster's message of "Fri, 23 Dec 2016 19:32:19 +0900")
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Bug Poster <bugzilla-mail-box@yandex.ru> writes:
> This is formula of Least Common Multiple:
>
> lcm(a, b) = |a * b| / gcd(a, b)
I agree, every textbook I can find defines lcm to return a positive
integer. Here's a patch, which hopefully someone will apply.
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From de52ee092bc0ab7c94d9270b9c3160c0923a68c0 Mon Sep 17 00:00:00 2001
From: "Peder O. Klingenberg" <peder@klingenberg.no>
Date: Sun, 5 Feb 2017 10:58:00 +0100
Subject: [PATCH] LCM is defined to return a positive integer.
Bug#25255:
* doc/misc/calc.texi (Combinatorial Functions): The product of
LCM and GCD is an absolute value.
* lisp/calc/calc-comb.el (calcFunc-lcm): Use absolute values.
---
doc/misc/calc.texi | 4 ++--
lisp/calc/calc-comb.el | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/doc/misc/calc.texi b/doc/misc/calc.texi
index baf46f7170..7bd060189c 100644
--- a/doc/misc/calc.texi
+++ b/doc/misc/calc.texi
@@ -19111,8 +19111,8 @@ Combinatorial Functions
@tindex lcm
The @kbd{k l} (@code{calc-lcm}) [@code{lcm}] command computes the
Least Common Multiple of two integers or fractions. The product of
-the LCM and GCD of two numbers is equal to the product of the
-numbers.
+the LCM and GCD of two numbers is equal to the absolute value of the
+product of the numbers.
@kindex k E
@pindex calc-extended-gcd
diff --git a/lisp/calc/calc-comb.el b/lisp/calc/calc-comb.el
index bc1ac315a0..c84ff23685 100644
--- a/lisp/calc/calc-comb.el
+++ b/lisp/calc/calc-comb.el
@@ -260,7 +260,7 @@ calcFunc-gcd
(defun calcFunc-lcm (a b)
(let ((g (calcFunc-gcd a b)))
(if (Math-numberp g)
- (math-div (math-mul a b) g)
+ (math-div (math-abs (math-mul a b)) g)
(list 'calcFunc-lcm a b))))
(defun calcFunc-egcd (a b) ; Knuth section 4.5.2
--
2.11.0
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--
...Peder...
next prev parent reply other threads:[~2017-02-05 10:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-23 10:32 bug#25255: Emacs calculator evalutes lcm to a negative number Bug Poster
2017-02-05 10:28 ` Peder O. Klingenberg [this message]
2017-02-24 1:30 ` Glenn Morris
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