Merge from origin/emacs-25

[gnu-emacs] / lisp / calc / calc-mtx.el

diff --git a/lisp/calc/calc-mtx.el b/lisp/calc/calc-mtx.el
index 9941c11ff14448229c340ae4f7328462799ed5de..a093832daaeb68f142802eea3a2ebf30e146aa8d 100644 (file)
--- a/lisp/calc/calc-mtx.el
+++ b/lisp/calc/calc-mtx.el
@@ -1,9 +1,8 @@
 ;;; calc-mtx.el --- matrix functions for Calc
 
-;; Copyright (C) 1990-1993, 2001-2011 Free Software Foundation, Inc.
+;; Copyright (C) 1990-1993, 2001-2016 Free Software Foundation, Inc.
 
 ;; Author: David Gillespie <daveg@synaptics.com>
-;; Maintainer: Jay Belanger <jay.p.belanger@gmail.com>
 
 ;; This file is part of GNU Emacs.
 
@@ -232,6 +231,20 @@
          (setq math-lud-cache (cons (cons m entry) math-lud-cache)))
        lud))))
 
+
+(defun math-lud-pivot-check (a)
+  "Determine a useful value for checking the size of potential pivots
+in LUD decomposition."
+  (cond ((eq (car-safe a) 'mod)
+         (if (and (math-integerp (nth 1 a))
+                  (math-integerp (nth 2 a))
+                  (eq (math-gcd (nth 1 a) (nth 2 a)) 1))
+             1
+           0))
+        (t
+         (math-abs-approx a))))
+
+
 ;;; Numerical Recipes section 2.3; implicit pivoting omitted.
 (defun math-do-matrix-lud (m)
   (let* ((lu (math-copy-matrix m))
@@ -261,7 +274,7 @@
                                            (nth j (nth k lu))))
                k (1+ k)))
        (setcar (nthcdr j (nth i lu)) sum)
-       (let ((dum (math-abs-approx sum)))
+       (let ((dum (math-lud-pivot-check sum)))
          (if (Math-lessp big dum)
              (setq big dum
                    imax i)))