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Forced symmetry in binomialCoefficientLog and added test cases for MathUtils. 

JIRA: MATH-242
Reported and patched by Christian Semrau

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@736288 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Phil Steitz 2009-01-21 11:30:36 +00:00
parent 944446a1a8
commit c5d148896f
3 changed files with 108 additions and 33 deletions
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16
src/java/org/apache/commons/math/util/MathUtils.java
View File

@ -323,19 +323,23 @@ public final class MathUtils {
return Math.log(binomialCoefficientDouble(n, k));
}
if (k > n / 2) {
return binomialCoefficientLog(n, n - k);
}
/*
* Sum logs for values that could overflow
*/
double logSum = 0;
// n!/k!
for (int i = k + 1; i <= n; i++) {
logSum += Math.log((double)i);
// n!/(n-k)!
for (int i = n - k + 1; i <= n; i++) {
logSum += Math.log((double) i);
}
// divide by (n-k)!
for (int i = 2; i <= n - k; i++) {
logSum -= Math.log((double)i);
// divide by k!
for (int i = 2; i <= k; i++) {
logSum -= Math.log((double) i);
}
return logSum;

3
src/site/xdoc/changes.xml
View File

@ -39,6 +39,9 @@ The <action> type attribute can be add,update,fix,remove.
</properties>
<body>
<release version="2.0" date="TBD" description="TBD">
<action dev="psteitz" type="update" issue="MATH-242" due-to="Christian Semrau">
Forced symmetry in binomialCoefficientLog and added test cases for MathUtils.
</action>
<action dev="psteitz" type="fix" issue="MATH-241" due-to="Christian Semrau">
Fixed error in binomial coefficient computation.
</action>

118
src/test/org/apache/commons/math/util/MathUtilsTest.java
View File

@ -62,6 +62,13 @@ public final class MathUtilsTest extends TestCase {
} else if ((k == 1) || (k == n - 1)) {
result = n;
} else {
// Reduce stack depth for larger values of n
if (k < n - 100) {
binomialCoefficient(n - 100, k);
}
if (k > 100) {
binomialCoefficient(n - 100, k - 100);
}
result = MathUtils.addAndCheck(binomialCoefficient(n - 1, k - 1),
binomialCoefficient(n - 1, k));
}
@ -119,6 +126,8 @@ public final class MathUtilsTest extends TestCase {
assertEquals(min, MathUtils.addAndCheck(0L, min));
assertEquals(1, MathUtils.addAndCheck(-1L, 2L));
assertEquals(1, MathUtils.addAndCheck(2L, -1L));
assertEquals(-3, MathUtils.addAndCheck(-2L, -1L));
assertEquals(min, MathUtils.addAndCheck(min + 1, -1L));
testAddAndCheckLongFailure(max, 1L);
testAddAndCheckLongFailure(min, -1L);
testAddAndCheckLongFailure(1L, max);
@ -165,8 +174,17 @@ public final class MathUtilsTest extends TestCase {
}
}
assertEquals(binomialCoefficient(34, 17), MathUtils
.binomialCoefficient(34, 17));
int[] n = { 34, 66, 100, 1500, 1500 };
int[] k = { 17, 33, 10, 1500 - 4, 4 };
for (int i = 0; i < n.length; i++) {
long expected = binomialCoefficient(n[i], k[i]);
assertEquals(n[i] + " choose " + k[i], expected,
MathUtils.binomialCoefficient(n[i], k[i]));
assertEquals(n[i] + " choose " + k[i], (double) expected,
MathUtils.binomialCoefficientDouble(n[i], k[i]), 0.0);
assertEquals("log(" + n[i] + " choose " + k[i] + ")", Math.log(expected),
MathUtils.binomialCoefficientLog(n[i], k[i]), 0.0);
}
}
/**
@ -191,9 +209,16 @@ public final class MathUtilsTest extends TestCase {
} catch (ArithmeticException ex) {
shouldThrow = true;
}
assertEquals(n+","+k, shouldThrow, didThrow);
assertEquals(n+","+k, exactResult, ourResult);
assertTrue(n+","+k, (n > 66 || !didThrow));
assertEquals(n + " choose " + k, exactResult, ourResult);
assertEquals(n + " choose " + k, shouldThrow, didThrow);
assertTrue(n + " choose " + k, (n > 66 || !didThrow));
if (!shouldThrow && exactResult > 1) {
assertEquals(n + " choose " + k, 1.,
MathUtils.binomialCoefficientDouble(n, k) / exactResult, 1e-10);
assertEquals(n + " choose " + k, 1,
MathUtils.binomialCoefficientLog(n, k) / Math.log(exactResult), 1e-10);
}
}
}
@ -213,14 +238,12 @@ public final class MathUtilsTest extends TestCase {
// Expected
}
// Larger values cannot be computed directly by our
// test implementation because of stack limitations,
// so we make little jumps to fill the cache.
for (int i = 2000; i <= 10000; i += 2000) {
ourResult = MathUtils.binomialCoefficient(i, 3);
exactResult = binomialCoefficient(i, 3);
assertEquals(exactResult, ourResult);
}
int n = 10000;
ourResult = MathUtils.binomialCoefficient(n, 3);
exactResult = binomialCoefficient(n, 3);
assertEquals(exactResult, ourResult);
assertEquals(1, MathUtils.binomialCoefficientDouble(n, 3) / exactResult, 1e-10);
assertEquals(1, MathUtils.binomialCoefficientLog(n, 3) / Math.log(exactResult), 1e-10);
}
@ -245,6 +268,26 @@ public final class MathUtilsTest extends TestCase {
} catch (IllegalArgumentException ex) {
;
}
try {
MathUtils.binomialCoefficient(-1, -2);
fail("expecting IllegalArgumentException");
} catch (IllegalArgumentException ex) {
;
}
try {
MathUtils.binomialCoefficientDouble(-1, -2);
fail("expecting IllegalArgumentException");
} catch (IllegalArgumentException ex) {
;
}
try {
MathUtils.binomialCoefficientLog(-1, -2);
fail("expecting IllegalArgumentException");
} catch (IllegalArgumentException ex) {
;
}
try {
MathUtils.binomialCoefficient(67, 30);
fail("expecting ArithmeticException");
@ -377,6 +420,14 @@ public final class MathUtilsTest extends TestCase {
assertEquals(3 * (1<<15), MathUtils.gcd(3 * (1<<20), 9 * (1<<15)));
assertEquals(Integer.MAX_VALUE, MathUtils.gcd(Integer.MAX_VALUE, 0));
// abs(Integer.MIN_VALUE) == Integer.MIN_VALUE
assertEquals(Integer.MIN_VALUE, MathUtils.gcd(Integer.MIN_VALUE, 0));
try {
MathUtils.gcd(Integer.MIN_VALUE, Integer.MIN_VALUE);
} catch (ArithmeticException expected) {
//
}
}
public void testHash() {
@ -459,6 +510,7 @@ public final class MathUtilsTest extends TestCase {
assertEquals(1.0, MathUtils.indicator(2.0), delta);
assertEquals(1.0, MathUtils.indicator(0.0), delta);
assertEquals(-1.0, MathUtils.indicator(-2.0), delta);
assertEquals(Double.NaN, MathUtils.indicator(Double.NaN));
}
public void testIndicatorFloat() {
@ -545,6 +597,8 @@ public final class MathUtilsTest extends TestCase {
assertEquals(min, MathUtils.mulAndCheck(1L, min));
assertEquals(0L, MathUtils.mulAndCheck(0L, max));
assertEquals(0L, MathUtils.mulAndCheck(0L, min));
assertEquals(1L, MathUtils.mulAndCheck(-1L, -1L));
assertEquals(min, MathUtils.mulAndCheck(min / 2, 2));
testMulAndCheckLongFailure(max, 2L);
testMulAndCheckLongFailure(2L, max);
testMulAndCheckLongFailure(min, 2L);
@ -864,35 +918,43 @@ public final class MathUtilsTest extends TestCase {
}
public void testSignByte() {
assertEquals((byte)1, MathUtils.indicator((byte)2));
assertEquals((byte)(-1), MathUtils.indicator((byte)(-2)));
assertEquals((byte) 1, MathUtils.sign((byte) 2));
assertEquals((byte) 0, MathUtils.sign((byte) 0));
assertEquals((byte) (-1), MathUtils.sign((byte) (-2)));
}
public void testSignDouble() {
double delta = 0.0;
assertEquals(1.0, MathUtils.indicator(2.0), delta);
assertEquals(-1.0, MathUtils.indicator(-2.0), delta);
assertEquals(1.0, MathUtils.sign(2.0), delta);
assertEquals(0.0, MathUtils.sign(0.0), delta);
assertEquals(-1.0, MathUtils.sign(-2.0), delta);
assertEquals(-0. / 0., MathUtils.sign(Double.NaN), delta);
}
public void testSignFloat() {
float delta = 0.0F;
assertEquals(1.0F, MathUtils.indicator(2.0F), delta);
assertEquals(-1.0F, MathUtils.indicator(-2.0F), delta);
assertEquals(1.0F, MathUtils.sign(2.0F), delta);
assertEquals(0.0F, MathUtils.sign(0.0F), delta);
assertEquals(-1.0F, MathUtils.sign(-2.0F), delta);
assertEquals(Float.NaN, MathUtils.sign(Float.NaN), delta);
}
public void testSignInt() {
assertEquals((int)1, MathUtils.indicator((int)(2)));
assertEquals((int)(-1), MathUtils.indicator((int)(-2)));
assertEquals((int) 1, MathUtils.sign((int) 2));
assertEquals((int) 0, MathUtils.sign((int) 0));
assertEquals((int) (-1), MathUtils.sign((int) (-2)));
}
public void testSignLong() {
assertEquals(1L, MathUtils.indicator(2L));
assertEquals(-1L, MathUtils.indicator(-2L));
assertEquals(1L, MathUtils.sign(2L));
assertEquals(0L, MathUtils.sign(0L));
assertEquals(-1L, MathUtils.sign(-2L));
}
public void testSignShort() {
assertEquals((short)1, MathUtils.indicator((short)2));
assertEquals((short)(-1), MathUtils.indicator((short)(-2)));
assertEquals((short) 1, MathUtils.sign((short) 2));
assertEquals((short) 0, MathUtils.sign((short) 0));
assertEquals((short) (-1), MathUtils.sign((short) (-2)));
}
public void testSinh() {
@ -909,6 +971,8 @@ public final class MathUtilsTest extends TestCase {
int big = Integer.MAX_VALUE;
int bigNeg = Integer.MIN_VALUE;
assertEquals(big, MathUtils.subAndCheck(big, 0));
assertEquals(bigNeg + 1, MathUtils.subAndCheck(bigNeg, -1));
assertEquals(-1, MathUtils.subAndCheck(bigNeg, -big));
try {
MathUtils.subAndCheck(big, -1);
fail("Expecting ArithmeticException");
@ -937,6 +1001,10 @@ public final class MathUtilsTest extends TestCase {
assertEquals(max, MathUtils.subAndCheck(max, 0));
assertEquals(min, MathUtils.subAndCheck(min, 0));
assertEquals(-max, MathUtils.subAndCheck(0, max));
assertEquals(min + 1, MathUtils.subAndCheck(min, -1));
// min == -1-max
assertEquals(-1, MathUtils.subAndCheck(-max - 1, -max));
assertEquals(max, MathUtils.subAndCheck(-1, -1 - max));
testSubAndCheckLongFailure(0L, min);
testSubAndCheckLongFailure(max, -1L);
testSubAndCheckLongFailure(min, 1L);