Add polynomial test.

3 files changed, 66 insertions, 4 deletions

diff --git a/libdimension/polynomial.c b/libdimension/polynomial.c
index f361d38..32dd922 100644
--- a/libdimension/polynomial.c
+++ b/libdimension/polynomial.c
@@ -80,7 +80,7 @@ dmnsn_real_degree(double poly[], size_t degree)
 static inline double
 dmnsn_improve_root(double poly[], size_t degree, double x)
 {
-  double error;
+  double dx;
   do {
     /* Calculate the value of the polynomial and its derivative at once */
     double p = poly[degree], dp = 0.0;
@@ -89,10 +89,9 @@ dmnsn_improve_root(double poly[], size_t degree, double x)
       p  = p*x  + poly[i];
     }
 
-    double dx = p/dp;
-    error = fabs(dx/x);
+    dx = p/dp;
     x -= dx;
-  } while (error > dmnsn_epsilon);
+  } while (fabs(dx) > dmnsn_epsilon);
 
   return x;
 }
diff --git a/tests/libdimension/Makefile.am b/tests/libdimension/Makefile.am
index f6918dc..252deba 100644
--- a/tests/libdimension/Makefile.am
+++ b/tests/libdimension/Makefile.am
@@ -22,6 +22,7 @@ INCLUDES = -I$(top_srcdir)/libdimension
 check_LTLIBRARIES = libdimension-tests.la
 check_PROGRAMS    = error-test                                                 \
                     warning-test                                               \
+                    polynomial-test                                            \
                     prtree-test                                                \
                     png-test                                                   \
                     gl-test                                                    \
@@ -54,6 +55,9 @@ error_test_LDADD   = libdimension-tests.la
 warning_test_SOURCES = warning.c
 warning_test_LDADD   = libdimension-tests.la
 
+polynomial_test_SOURCES = polynomial.c
+polynomial_test_LDADD   = libdimension-tests.la
+
 prtree_test_SOURCES = prtree.c
 prtree_test_LDADD   = libdimension-tests.la
 
diff --git a/tests/libdimension/polynomial.c b/tests/libdimension/polynomial.c
new file mode 100644
index 0000000..230a1a7
--- /dev/null
+++ b/tests/libdimension/polynomial.c
@@ -0,0 +1,59 @@
+/*************************************************************************
+ * Copyright (C) 2010 Tavian Barnes <tavianator@gmail.com>               *
+ *                                                                       *
+ * This file is part of The Dimension Test Suite.                        *
+ *                                                                       *
+ * The Dimension Test Suite is free software; you can redistribute it    *
+ * and/or modify it under the terms of the GNU General Public License as *
+ * published by the Free Software Foundation; either version 3 of the    *
+ * License, or (at your option) any later version.                       *
+ *                                                                       *
+ * The Dimension Test Suite is distributed in the hope that it will be   *
+ * useful, but WITHOUT ANY WARRANTY; without even the implied warranty   *
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  *
+ * General Public License for more details.                              *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+/*
+ * Basic tests of PR-trees
+ */
+
+#include "dimension.h"
+#include <stddef.h>
+#include <stdio.h>
+
+int
+main()
+{
+  double poly[6], x[5];
+  // poly[] = (x + 1)*(x - 1.2345)*(x - 2.3456)*(x - 5)*(x - 100)
+  poly[5] =  1.0;
+  poly[4] = -107.5801;
+  poly[3] =  770.2260432;
+  poly[2] = -1215.2863928;
+  poly[1] = -646.270936;
+  poly[0] =  1447.8216;
+
+  size_t n = dmnsn_solve_polynomial(poly, 5, x);
+  if (n != 4) {
+    fprintf(stderr,
+            "--- Wrong number of roots found (%zu, should be %u) ---\n",
+            n, 4);
+    return EXIT_FAILURE;
+  }
+
+  for (size_t i = 0; i < n; ++i) {
+    double evmin = dmnsn_evaluate_polynomial(poly, 5, x[i] - dmnsn_epsilon);
+    double ev    = dmnsn_evaluate_polynomial(poly, 5, x[i]);
+    double evmax = dmnsn_evaluate_polynomial(poly, 5, x[i] + dmnsn_epsilon);
+    if (fabs(evmin) < ev || fabs(evmax) < ev) {
+      fprintf(stderr, "--- Root %.15g is inaccurate! ---\n", x[i]);
+      return EXIT_FAILURE;
+    }
+  }
+
+  return EXIT_SUCCESS;
+}