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[Emacs-diffs] emacs-26 73e1727: Fix linear equation system solving in Ca
From: |
Mattias Engdegård |
Subject: |
[Emacs-diffs] emacs-26 73e1727: Fix linear equation system solving in Calc (bug#35374) |
Date: |
Mon, 23 Sep 2019 05:52:53 -0400 (EDT) |
branch: emacs-26
commit 73e1727c405214086bb3a0647c91855e1b0853c2
Author: Mattias Engdegård <address@hidden>
Commit: Mattias Engdegård <address@hidden>
Fix linear equation system solving in Calc (bug#35374)
* lisp/calc/calcalg2.el (math-try-solve-for):
To solve Ax^n=0 where A is a nonzero constant and x the variable to
solve for, solve x^n=0 instead of solving A=0 (which obviously fails)
or something equally stupid.
* test/lisp/calc/calc-tests.el (calc-test-solve-linear-system): New.
---
lisp/calc/calcalg2.el | 6 +++
test/lisp/calc/calc-tests.el | 103 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 109 insertions(+)
diff --git a/lisp/calc/calcalg2.el b/lisp/calc/calcalg2.el
index 18243bf..2a71663 100644
--- a/lisp/calc/calcalg2.el
+++ b/lisp/calc/calcalg2.el
@@ -2417,6 +2417,12 @@
((= (length math-t1) 2)
(apply 'math-solve-linear
(car math-t2) math-try-solve-sign math-t1))
+ ((= (length math-t1) 1)
+ ;; Constant polynomial.
+ (if (eql (nth 2 math-t2) 1)
+ nil ; No possible solution.
+ ;; Root of the factor, if any.
+ (math-try-solve-for (nth 2 math-t2) 0 nil t)))
(math-solve-full
(math-poly-all-roots (car math-t2) math-t1))
(calc-symbolic-mode nil)
diff --git a/test/lisp/calc/calc-tests.el b/test/lisp/calc/calc-tests.el
index 8afec59..3f0b65a 100644
--- a/test/lisp/calc/calc-tests.el
+++ b/test/lisp/calc/calc-tests.el
@@ -138,6 +138,109 @@ An existing calc stack is reused, otherwise a new one is
created."
(nth 1 (calcFunc-cos 1)))
0 4))))))
+(ert-deftest calc-test-solve-linear-system ()
+ "Test linear system solving (bug#35374)."
+ ;; x + y = 3
+ ;; 2x - 3y = -4
+ ;; with the unique solution x=1, y=2
+ (should (equal
+ (calcFunc-solve
+ '(vec
+ (calcFunc-eq (+ (var x var-x) (var y var-y)) 3)
+ (calcFunc-eq (- (* 2 (var x var-x)) (* 3 (var y var-y))) -4))
+ '(vec (var x var-x) (var y var-y)))
+ '(vec (calcFunc-eq (var x var-x) 1)
+ (calcFunc-eq (var y var-y) 2))))
+
+ ;; x + y = 1
+ ;; x + y = 2
+ ;; has no solution
+ (should (equal
+ (calcFunc-solve
+ '(vec
+ (calcFunc-eq (+ (var x var-x) (var y var-y)) 1)
+ (calcFunc-eq (+ (var x var-x) (var y var-y)) 2))
+ '(vec (var x var-x) (var y var-y)))
+ '(calcFunc-solve
+ (vec
+ (calcFunc-eq (+ (var x var-x) (var y var-y)) 1)
+ (calcFunc-eq (+ (var x var-x) (var y var-y)) 2))
+ (vec (var x var-x) (var y var-y)))))
+ ;; x - y = 1
+ ;; x + y = 1
+ ;; with the unique solution x=1, y=0
+ (should (equal
+ (calcFunc-solve
+ '(vec
+ (calcFunc-eq (- (var x var-x) (var y var-y)) 1)
+ (calcFunc-eq (+ (var x var-x) (var y var-y)) 1))
+ '(vec (var x var-x) (var y var-y)))
+ '(vec (calcFunc-eq (var x var-x) 1)
+ (calcFunc-eq (var y var-y) 0))))
+ ;; 2x - 3y + z = 5
+ ;; x + y - 2z = 0
+ ;; -x + 2y + 3z = -3
+ ;; with the unique solution x=1, y=-1, z=0
+ (should (equal
+ (calcFunc-solve
+ '(vec
+ (calcFunc-eq
+ (+ (- (* 2 (var x var-x)) (* 3 (var y var-y))) (var z var-z))
+ 5)
+ (calcFunc-eq
+ (- (+ (var x var-x) (var y var-y)) (* 2 (var z var-z)))
+ 0)
+ (calcFunc-eq
+ (+ (- (* 2 (var y var-y)) (var x var-x)) (* 3 (var z var-z)))
+ -3))
+ '(vec (var x var-x) (var y var-y) (var z var-z)))
+ ;; The `float' forms in the result are just artefacts of Calc's
+ ;; current solver; it should be fixed to produce exact (integral)
+ ;; results in this case.
+ '(vec (calcFunc-eq (var x var-x) (float 1 0))
+ (calcFunc-eq (var y var-y) (float -1 0))
+ (calcFunc-eq (var z var-z) 0))))
+ ;; x = y + 1
+ ;; x = y
+ ;; has no solution
+ (should (equal
+ (calcFunc-solve
+ '(vec
+ (calcFunc-eq (var x var-x) (+ (var y var-y) 1))
+ (calcFunc-eq (var x var-x) (var y var-y)))
+ '(vec (var x var-x) (var y var-y)))
+ '(calcFunc-solve
+ (vec
+ (calcFunc-eq (var x var-x) (+ (var y var-y) 1))
+ (calcFunc-eq (var x var-x) (var y var-y)))
+ (vec (var x var-x) (var y var-y)))))
+ ;; x + y + z = 6
+ ;; x + y = 3
+ ;; x - y = 1
+ ;; with the unique solution x=2, y=1, z=3
+ (should (equal
+ (calcFunc-solve
+ '(vec
+ (calcFunc-eq (+ (+ (var x var-x) (var y var-y)) (var z var-z)) 6)
+ (calcFunc-eq (+ (var x var-x) (var y var-y)) 3)
+ (calcFunc-eq (- (var x var-x) (var y var-y)) 1))
+ '(vec (var x var-x) (var y var-y) (var z var-z)))
+ '(vec
+ (calcFunc-eq (var x var-x) 2)
+ (calcFunc-eq (var y var-y) 1)
+ (calcFunc-eq (var z var-z) 3))))
+ ;; x = 3
+ ;; x + 4y^2 = 3 (ok, so this one isn't linear)
+ ;; with the unique (double) solution x=3, y=0
+ (should (equal
+ (calcFunc-solve
+ '(vec
+ (calcFunc-eq (var x var-x) 3)
+ (calcFunc-eq (+ (var x var-x) (* 4 (^ (var y var-y) 2))) 3))
+ '(vec (var x var-x) (var y var-y)))
+ '(vec (calcFunc-eq (var x var-x) 3)
+ (calcFunc-eq (var y var-y) 0)))))
+
(provide 'calc-tests)
;;; calc-tests.el ends here
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