From 577d01982080e181edeba5172d5a7e007170f4e3 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Mon, 3 Feb 2014 12:14:44 -0500
Subject: Fix a bug in cubic polynomial solver, and add more tests.

---
 libdimension/polynomial.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

(limited to 'libdimension/polynomial.c')

diff --git a/libdimension/polynomial.c b/libdimension/polynomial.c
index 9491861..3f64091 100644
--- a/libdimension/polynomial.c
+++ b/libdimension/polynomial.c
@@ -358,9 +358,9 @@ dmnsn_solve_cubic(double poly[4], double x[3])
     x[0] = -bdiv3;
   } else {
     /* Two real roots; one duplicate */
-    double t1 = 3.0*q/p, t2 = -t1/2.0;
-    x[0] = dmnsn_max(t1, t2);
-    x[1] = dmnsn_min(t1, t2);
+    double t1 = -(3.0*q)/(2.0*p), t2 = -2.0*t1;
+    x[0] = dmnsn_max(t1, t2) - bdiv3;
+    x[1] = dmnsn_min(t1, t2) - bdiv3;
     if (x[1] >= dmnsn_epsilon)
       return 2;
   }
-- 
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