add GTest infrastructure and port first mathematical tests from Java
- Add Google Test via CMake FetchContent (v1.14.0) - Add clausen.hpp: Clausen integral, Lobachevsky function, Im(Li2) - Add hyper_ideal_utility.hpp: generalized and ideal-vertex hyperbolic tetrahedron volume formulas using Eigen for the 4x4 Gram determinant - Port ClausenTest (5 tests) and HyperIdealUtilityTest (8 tests) from Java/JUnit — all 13 pass with same tolerances as the Java originals - Fix pre-existing VIEWER/viewer case mismatch in CMakeLists.txt Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Tarik Moussa
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code/include/clausen.hpp
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179
code/include/clausen.hpp
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#pragma once
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// Clausen integral, Lobachevsky function, and Im(Li2).
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// Ported from de.varylab.discreteconformal.functional.Clausen (Java).
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// Original algorithm: Boris Springborn, Stefan Sechelmann (TU Berlin).
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#include <cmath>
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#include <complex>
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#include <cstdlib>
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namespace conformallab {
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namespace detail {
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// Evaluate a Chebyshev series at x using n terms.
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// Corresponds to Java Clausen.csevl().
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inline double csevl(double x, const double* cs, int n) noexcept {
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double b2 = 0.0, b1 = 0.0, b0 = 0.0;
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const double twox = 2.0 * x;
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while (n-- > 0) {
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b2 = b1;
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b1 = b0;
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b0 = twox * b1 - b2 + cs[n];
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}
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return 0.5 * (b0 - b2);
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}
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// Count Chebyshev terms needed so truncation error <= eta.
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// Corresponds to Java Clausen.inits().
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inline int inits(const double* series, int n, double eta) noexcept {
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double err = 0.0;
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while (err <= eta && n-- != 0) {
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err += std::abs(series[n]);
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}
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return n;
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}
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// Chebyshev expansion of `cl(t)/t + log(t)` around Pi/6.
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inline const double* clpi6() noexcept {
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static const double a[] = {
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2 * 1.0057346496467363858,
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.0076523796971586786263,
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.0019223823523180480014,
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.53333368801173950429e-5,
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.68684944849366102659e-6,
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.63769755654413855855e-8,
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.57069363812137970721e-9,
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.87936343137236194448e-11,
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.62365831120408524691e-12,
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.12996625954032513221e-13,
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.78762044080566097484e-15,
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.20080243561666612900e-16,
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.10916495826127475499e-17,
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.32027217200949691956e-19,
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};
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return a;
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}
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// Chebyshev expansion around Pi/2.
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inline const double* clpi2() noexcept {
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static const double a[] = {
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2 * .017492908851746863924 + 2 * 1.0057346496467363858,
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.023421240075284860656 + .0076523796971586786263,
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.0060025281630108248332 + .0019223823523180480014,
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.000085934211448718844330 + .53333368801173950429e-5,
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.000012155033501044820317 + .68684944849366102659e-6,
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.46587486310623464413e-6 + .63769755654413855855e-8,
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.50732554559130493329e-7 + .57069363812137970721e-9,
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.28794458754760053792e-8 + .87936343137236194448e-11,
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.27792370776596244150e-9 + .62365831120408524691e-12,
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.19340423475636663004e-10 + .12996625954032513221e-13,
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.17726134256574610202e-11 + .78762044080566097484e-15,
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.13811355237660945692e-12 + .20080243561666612900e-16,
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.12433074161771699487e-13 + .10916495826127475499e-17,
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.10342683357723940535e-14 + .32027217200949691956e-19,
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.92910354101990447850e-16,
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.80428334724548559541e-17,
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.72598441354406482972e-18,
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.64475701884829384587e-19,
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.58630185185185185187e-20,
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};
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return a;
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}
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// Chebyshev expansion of `-cl(Pi-t)/(Pi-t) + log(2)` around 5*Pi/6.
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inline const double* cl5pi6() noexcept {
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static const double a[] = {
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2 * .017492908851746863924,
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.023421240075284860656,
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.0060025281630108248332,
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.000085934211448718844330,
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.000012155033501044820317,
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.46587486310623464413e-6,
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.50732554559130493329e-7,
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.28794458754760053792e-8,
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.27792370776596244150e-9,
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.19340423475636663004e-10,
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.17726134256574610202e-11,
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.13811355237660945692e-12,
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.12433074161771699487e-13,
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.10342683357723940535e-14,
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.92910354101990447850e-16,
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.80428334724548559541e-17,
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.72598441354406482972e-18,
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.64475701884829384587e-19,
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.58630185185185185187e-20,
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};
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return a;
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}
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// Machine epsilon for double (IEEE 754).
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constexpr double kMachEps = 1.1102230246251565e-16;
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constexpr double kLn2 = 0.693147180559945309417232121458;
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// Number of Chebyshev terms for each expansion (computed like Java static init).
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inline int nclpi6() noexcept {
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static const int n = inits(clpi6(), 14, kMachEps / 10.0);
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return n;
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}
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inline int nclpi2() noexcept {
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static const int n = inits(clpi2(), 19, kMachEps / 10.0);
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return n;
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}
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inline int ncl5pi6() noexcept {
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static const int n = inits(cl5pi6(), 19, kMachEps / 10.0);
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return n;
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}
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} // namespace detail
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// Clausen's integral Cl2(x) = -integral_0^x log|2 sin(t/2)| dt.
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// High-precision Chebyshev implementation.
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// Corresponds to Java Clausen.clausen2().
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inline double clausen2(double x) noexcept {
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using namespace detail;
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constexpr double pi = 3.14159265358979323846264338328;
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constexpr double two_pi = 2.0 * pi;
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int rh = 0;
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x = std::fmod(x, two_pi);
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if (x < 0.0) x += two_pi;
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if (x > pi) { rh = 1; x = two_pi - x; }
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double f;
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if (x == 0.0) {
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f = 0.0;
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} else if (x <= pi / 3.0) {
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f = csevl(x * (6.0 / pi) - 1.0, clpi6(), nclpi6()) * x - x * std::log(x);
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} else if (x <= 2.0 * pi / 3.0) {
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f = csevl(x * (3.0 / pi) - 1.0, clpi2(), nclpi2()) * x - x * std::log(x);
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} else {
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f = (kLn2 - csevl(5.0 - x * (6.0 / pi), cl5pi6(), ncl5pi6())) * (pi - x);
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}
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return rh ? -f : f;
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}
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// Milnor's Lobachevsky function Л(x) = Cl2(2x)/2.
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// Corresponds to Java Clausen.Л().
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inline double Lobachevsky(double x) noexcept {
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constexpr double pi = 3.14159265358979323846264338328;
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x = std::fmod(x, pi);
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if (x <= 0.0) x += pi;
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return clausen2(2.0 * x) / 2.0;
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}
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// Imaginary part of the dilogarithm Im(Li2(z)).
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// Corresponds to Java Clausen.ImLi2().
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inline double ImLi2(std::complex<double> z) noexcept {
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auto a = std::log(1.0 - std::conj(z)); // log(1 - conj(z))
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auto b = std::log(1.0 - z); // log(1 - z)
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double x = std::log(std::abs(z));
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double y = 0.5 * (a - b).imag();
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double phi = std::arg(z);
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return y * x + 0.5 * (clausen2(2.0 * y)
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- clausen2(2.0 * (y + phi))
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+ clausen2(2.0 * phi));
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}
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} // namespace conformallab
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