1 // ******************************************************************************
2 //
3 // Title: Force Field X.
4 // Description: Force Field X - Software for Molecular Biophysics.
5 // Copyright: Copyright (c) Michael J. Schnieders 2001-2024.
6 //
7 // This file is part of Force Field X.
8 //
9 // Force Field X is free software; you can redistribute it and/or modify it
10 // under the terms of the GNU General Public License version 3 as published by
11 // the Free Software Foundation.
12 //
13 // Force Field X is distributed in the hope that it will be useful, but WITHOUT
14 // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
15 // FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
16 // details.
17 //
18 // You should have received a copy of the GNU General Public License along with
19 // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
20 // Place, Suite 330, Boston, MA 02111-1307 USA
21 //
22 // Linking this library statically or dynamically with other modules is making a
23 // combined work based on this library. Thus, the terms and conditions of the
24 // GNU General Public License cover the whole combination.
25 //
26 // As a special exception, the copyright holders of this library give you
27 // permission to link this library with independent modules to produce an
28 // executable, regardless of the license terms of these independent modules, and
29 // to copy and distribute the resulting executable under terms of your choice,
30 // provided that you also meet, for each linked independent module, the terms
31 // and conditions of the license of that module. An independent module is a
32 // module which is not derived from or based on this library. If you modify this
33 // library, you may extend this exception to your version of the library, but
34 // you are not obligated to do so. If you do not wish to do so, delete this
35 // exception statement from your version.
36 //
37 // ******************************************************************************
38 package ffx.numerics.special;
39
40 import java.util.Arrays;
41 import java.util.Collection;
42
43 import ffx.utilities.FFXTest;
44 import org.junit.Assert;
45 import org.junit.Test;
46 import org.junit.runner.RunWith;
47 import org.junit.runners.Parameterized;
48 import org.junit.runners.Parameterized.Parameters;
49
50 /** @author Michael J. Schnieders */
51 @RunWith(Parameterized.class)
52 public class ErfTest extends FFXTest {
53
54 /**
55 * Java double precision follows the IEEE 754 Binary Floating-Point Arithmetic standard. Each
56 * double consumes 8 bytes of storage and offers 52 binary digits of precision (14-15 decimal
57 * digits). This implementation of Erf passes for a tolerance of 1.0e-15 and (as one might expect)
58 * fails using 1.0e-16.
59 */
60 private static final double tolerance = 1.0e-15;
61
62 private final String info;
63 private final double x;
64 private final double expected;
65
66 public ErfTest(String info, double x, double expected) {
67 this.info = info;
68 this.x = x;
69 this.expected = expected;
70 }
71
72 /**
73 * The expected values were found to 20 decimal points of precision using Mathematica:
74 * Erf[SetPrecision[x, 20]] Erfc[SetPrecision[x, 20]]
75 */
76 @Parameters
77 public static Collection<Object[]> data() {
78 return Arrays.asList(
79 new Object[][] {
80 {"Test 0.0", 0.0e0, 0.0e0},
81 {"Test 0.1; below the first branch point.", 0.1e0, 0.1124629160182848984e0},
82 {"Test 0.46875; at the first branch point.", 0.46875e0, 0.4926134732179379916e0},
83 {"Test 1.0; between the branch points.", 1.0e0, 0.842700792949714869e0},
84 {"Test 4.0; at the second branch point.", 4.0e0, 1.0e0 - 1.5417257900280018852e-8},
85 {"Test 5.0; above the second branch point.", 5.0e0, 1.0e0 - 1.5374597944280348502e-12}
86 });
87 }
88
89 /** Test of erf method, of class Erf. */
90 @Test
91 public void testErf() {
92 double actual = Erf.erf(x);
93 Assert.assertEquals(info, expected, actual, tolerance);
94 }
95
96 /** Test of erfc method, of class Erf. */
97 @Test
98 public void testErfc() {
99 double actual = Erf.erfc(x);
100 Assert.assertEquals(info, 1.0 - expected, actual, tolerance);
101 }
102 }