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aherbert pushed a commit to branch master
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commit 4dd3fc82b1017834c2947682e20f2a13e92082c4
Author: aherbert <aherb...@apache.org>
AuthorDate: Wed Dec 18 21:34:21 2019 +0000
Updated sinh/asinh using an overflow/underflow safe method.
---
.../apache/commons/numbers/complex/Complex.java | 218 +++++++++++++++++++--
.../commons/numbers/complex/CReferenceTest.java | 2 +-
2 files changed, 208 insertions(+), 12 deletions(-)
diff --git
a/commons-numbers-complex/src/main/java/org/apache/commons/numbers/complex/Complex.java
b/commons-numbers-complex/src/main/java/org/apache/commons/numbers/complex/Complex.java
index 3d5f264..feb777c 100644
---
a/commons-numbers-complex/src/main/java/org/apache/commons/numbers/complex/Complex.java
+++
b/commons-numbers-complex/src/main/java/org/apache/commons/numbers/complex/Complex.java
@@ -78,6 +78,36 @@ public final class Complex implements Serializable {
/** Base 10 logarithm of 2 (log10(2)). */
private static final double LOG10_2 = Math.log10(2);
+ /** Crossover point to switch computation for asin factor A. */
+ private static final double A_CROSSOVER = 10;
+ /** Crossover point to switch computation for asin factor B. */
+ private static final double B_CROSSOVER = 0.6471;
+ /**
+ * The safe maximum double value {@code x} to avoid loss of precision in
asin.
+ * Equal to sqrt(M) / 8 in the Hull, et al with M the largest normalised
floating-point value.
+ */
+ private static final double SAFE_MAX = Math.sqrt(Double.MAX_VALUE) / 8;
+ /**
+ * The safe minimum double value {@code x} to avoid loss of
precision/underflow in asin.
+ * Equal to sqrt(u) * 4 in the Hull, et al with u the smallest normalised
floating-point value.
+ */
+ private static final double SAFE_MIN = Math.sqrt(Double.MIN_NORMAL) * 4;
+ /** Exponent offset in IEEE754 representation. */
+ private static final long EXPONENT_OFFSET = 1023L;
+ /**
+ * Largest double-precision floating-point number such that
+ * {@code 1 + EPSILON} is numerically equal to 1. This value is an upper
+ * bound on the relative error due to rounding real numbers to double
+ * precision floating-point numbers.
+ *
+ * <p>In IEEE 754 arithmetic, this is 2<sup>-53</sup>.</p>
+ *
+ * <p>Copied from o.a.c.numbers.core.Precision
+ *
+ * @see <a href="http://en.wikipedia.org/wiki/Machine_epsilon";>Machine
epsilon</a>
+ */
+ public static final double EPSILON =
Double.longBitsToDouble((EXPONENT_OFFSET - 53L) << 52);
+
/** Serializable version identifier. */
private static final long serialVersionUID = 20180201L;
@@ -1312,18 +1342,162 @@ public final class Complex implements Serializable {
* </code>
* </pre>
*
- * <p>As per the C.99 standard this function is computed using the
trigonomic identity:</p>
+ * <p>This is implemented using real {@code x} and imaginary {@code y}
parts:</p>
* <pre>
- * asin(z) = -i asinh(iz)
+ * <code>
+ * asin(z) = asin(B) + i sign(y)log(A + sqrt(A<sup>2</sup>-1))
+ * A = 0.5 [ sqrt((x+1)<sup>2</sup>+y<sup>2</sup>) +
sqrt((x-1)<sup>2</sup>+y<sup>2</sup>) ]
+ * B = 0.5 [ sqrt((x+1)<sup>2</sup>+y<sup>2</sup>) -
sqrt((x-1)<sup>2</sup>+y<sup>2</sup>) ]
+ * sign(y) = {@link Math#copySign(double,double) copySign(1.0, y)}
+ * </code>
* </pre>
*
+ * <p>The implementation is based on the method described in:</p>
+ * <blockquote>
+ * T E Hull, Thomas F Fairgrieve and Ping Tak Peter Tang (1997)
+ * Implementing the complex Arcsine and Arccosine Functions using
Exception Handling.
+ * ACM Transactions on Mathematical Software, Vol 23, No 3, pp 299-335.
+ * </blockquote>
+ *
+ * <p>The code has been adapted from the <a
href="https://www.boost.org/";>Boost</a>
+ * {@code c++} implementation {@code <boost/math/complex/asin.hpp>}. The
function is well
+ * defined over the entire complex number range, and produces accurate
values even at the
+ * extremes due to special handling of overflow and underflow
conditions.</p>
+ *
* @return the inverse sine of this complex number
*/
public Complex asin() {
- // Define in terms of asinh
- // asin(z) = -i asinh(iz)
- // Multiply this number by I, compute asinh, then multiply by back
- return asinh(-imaginary, real, Complex::multiplyNegativeI);
+ return asin(real, imaginary, Complex::ofCartesian);
+ }
+
+ /**
+ * Compute the inverse sine of the complex number.
+ *
+ * <p>This function exists to allow implementation of the identity
+ * {@code asinh(z) = -i asin(iz)}.<p>
+ *
+ * <p>The code has been adapted from the <a
href="https://www.boost.org/";>Boost</a>
+ * {@code c++} implementation {@code <boost/math/complex/asin.hpp>}.</p>
+ *
+ * @param real Real part.
+ * @param imaginary Imaginary part.
+ * @param constructor Constructor.
+ * @return the inverse sine of this complex number
+ */
+ private static Complex asin(double real, double imaginary,
ComplexConstructor constructor) {
+ // Compute with positive values and determine sign at the end
+ double x = Math.abs(real);
+ double y = Math.abs(imaginary);
+ // The result (without sign correction)
+ double re;
+ double im;
+
+ // Handle C99 special cases
+ if (Double.isNaN(x)) {
+ if (isPosInfinite(y)) {
+ re = x;
+ im = y;
+ } else {
+ // No-use of the input constructor
+ return NAN;
+ }
+ } else if (Double.isNaN(y)) {
+ if (x == 0) {
+ re = 0;
+ im = y;
+ } else if (isPosInfinite(x)) {
+ re = y;
+ im = x;
+ } else {
+ // No-use of the input constructor
+ return NAN;
+ }
+ } else if (isPosInfinite(x)) {
+ re = isPosInfinite(y) ? PI_OVER_4 : PI_OVER_2;
+ im = x;
+ } else if (isPosInfinite(y)) {
+ re = 0;
+ im = y;
+ } else {
+ // Special case for real numbers:
+ if (y == 0 && x <= 1) {
+ return constructor.create(Math.asin(real), imaginary);
+ }
+
+ double xp1 = x + 1;
+ double xm1 = x - 1;
+
+ if ((x < SAFE_MAX) && (x > SAFE_MIN) && (y < SAFE_MAX) && (y >
SAFE_MIN)) {
+ double yy = y * y;
+ double r = Math.sqrt(xp1 * xp1 + yy);
+ double s = Math.sqrt(xm1 * xm1 + yy);
+ double a = 0.5 * (r + s);
+ double b = x / a;
+
+ if (b <= B_CROSSOVER) {
+ re = Math.asin(b);
+ } else {
+ double apx = a + x;
+ if (x <= 1) {
+ re = Math.atan(x / Math.sqrt(0.5 * apx * (yy / (r +
xp1) + (s - xm1))));
+ } else {
+ re = Math.atan(x / (y * Math.sqrt(0.5 * (apx / (r +
xp1) + apx / (s + xm1)))));
+ }
+ }
+
+ if (a <= A_CROSSOVER) {
+ double am1;
+ if (x < 1) {
+ am1 = 0.5 * (yy / (r + xp1) + yy / (s - xm1));
+ } else {
+ am1 = 0.5 * (yy / (r + xp1) + (s + xm1));
+ }
+ im = Math.log1p(am1 + Math.sqrt(am1 * (a + 1)));
+ } else {
+ im = Math.log(a + Math.sqrt(a * a - 1));
+ }
+ } else {
+ // Hull et al: Exception handling code from figure 3
+ if (y <= (EPSILON * Math.abs(xm1))) {
+ if (x < 1) {
+ re = Math.asin(x);
+ im = y / Math.sqrt(-xp1 * xm1);
+ } else {
+ re = PI_OVER_2;
+ if ((Double.MAX_VALUE / xp1) > xm1) {
+ // xp1 * xm1 won't overflow:
+ im = Math.log1p(xm1 + Math.sqrt(xp1 * xm1));
+ } else {
+ im = LN_2 + Math.log(x);
+ }
+ }
+ } else if (y <= SAFE_MIN) {
+ // Hull et al: Assume x == 1.
+ // True if:
+ // E^2 > 8*sqrt(u)
+ //
+ // E = Machine epsilon: (1 + epsilon) = 1
+ // u = Double.MIN_NORMAL
+ re = PI_OVER_2 - Math.sqrt(y);
+ im = Math.sqrt(y);
+ } else if (EPSILON * y - 1 >= x) {
+ // Possible underflow:
+ re = x / y;
+ im = LN_2 + Math.log(y);
+ } else if (x > 1) {
+ re = Math.atan(x / y);
+ double xoy = x / y;
+ im = LN_2 + Math.log(y) + 0.5 * Math.log1p(xoy * xoy);
+ } else {
+ double a = Math.sqrt(1 + y * y);
+ // Possible underflow:
+ re = x / a;
+ im = 0.5 * Math.log1p(2 * y * (y + a));
+ }
+ }
+ }
+
+ return constructor.create(changeSign(re, real), changeSign(im,
imaginary));
}
/**
@@ -1361,17 +1535,27 @@ public final class Complex implements Serializable {
*
* <p>This is an odd function: {@code f(z) = -f(-z)}.
*
+ * <p>This function is computed using the trigonomic identity:</p>
+ * <pre>
+ * asinh(z) = -i asin(iz)
+ * </pre>
+ *
* @return the inverse hyperbolic sine of this complex number
*/
public Complex asinh() {
- return asinh(real, imaginary, Complex::ofCartesian);
+ // Define in terms of asin
+ // asinh(z) = -i asin(iz)
+ // Note: This is the opposite the the identity defined in the C.99
standard:
+ // asin(z) = -i asinh(iz)
+ // Multiply this number by I, compute asin, then multiply by back
+ return asin(-imaginary, real, Complex::multiplyNegativeI);
}
/**
* Compute the inverse hyperbolic sine of the complex number.
*
* <p>This function exists to allow implementation of the identity
- * {@code sin(z) = -i sinh(iz)}.<p>
+ * {@code asin(z) = -i asinh(iz)}.<p>
*
* @param real Real part.
* @param imaginary Imaginary part.
@@ -1460,7 +1644,7 @@ public final class Complex implements Serializable {
* Compute the inverse hyperbolic tangent of this complex number.
*
* <p>This function exists to allow implementation of the identity
- * {@code sin(z) = -i sinh(iz)}.<p>
+ * {@code atan(z) = -i atanh(iz)}.<p>
*
* @param real Real part.
* @param imaginary Imaginary part.
@@ -1962,7 +2146,7 @@ public final class Complex implements Serializable {
* <ul>
* <li>{@code |a| = }{@link Math#abs}(a)
* <li>{@code |a + b i| = }{@link Complex#abs}(a + b i)
- * <li>{@code sign(b) = }{@link Math#copySign(double,double)
copySign(1.0, b)}
+ * <li>{@code sign(b) = }{@link Math#copySign(double,double) copySign(1.0,
b)}
* </ul>
*
* @return the square root of {@code this}.
@@ -2320,12 +2504,24 @@ public final class Complex implements Serializable {
}
/**
+ * Check that a value is positive infinity. Used to replace {@link
Double#isInfinite()}
+ * when the input value is known to be positive (i.e. in the case where it
have been
+ * set using {@link Math#abs(double)}).
+ *
+ * @param d Value.
+ * @return {@code true} if {@code d} is +inf.
+ */
+ private static boolean isPosInfinite(double d) {
+ return d == Double.POSITIVE_INFINITY;
+ }
+
+ /**
* Create a complex number given the real and imaginary parts, then
multiply by {@code -i}.
* This is used in functions that implement trigonomic identities. It is
the functional
* equivalent of:
*
* <pre>
- * z = new Complex(real, imaginary).multiply(new Complex(0, -1));
+ * z = new Complex(real, imaginary).multiplyImaginary(-1);
* </pre>
*
* @param real Real part.
diff --git
a/commons-numbers-complex/src/test/java/org/apache/commons/numbers/complex/CReferenceTest.java
b/commons-numbers-complex/src/test/java/org/apache/commons/numbers/complex/CReferenceTest.java
index 57ad59f..0f944b4 100644
---
a/commons-numbers-complex/src/test/java/org/apache/commons/numbers/complex/CReferenceTest.java
+++
b/commons-numbers-complex/src/test/java/org/apache/commons/numbers/complex/CReferenceTest.java
@@ -278,7 +278,7 @@ public class CReferenceTest {
@Test
public void testAsinh() {
// Odd function: negative real cases defined by positive real cases
- assertOperation("asinh", Complex::asinh, 1);
+ assertOperation("asinh", Complex::asinh, 3);
}
@Test
