start using libformfactor

Polyhedron, associated classes, and some tests moved to external library.

Tests/SingleUse/ff-triangle.cpp

-#include "Base/Math/Constants.h"
-#include "Sample/LibFF/PolyhedralComponents.h"
-#include "Tests/GTestWrapper/google_test.h"
-#include <cstdio>
-
-//! Ad-hoc test of triangle form factor.
-//!
-//! Used while preparing polyhedral form factor manuscript for publication - JWu, dec 2020.
-//!
-//! To reactivate this code, just move in to ../UnitTest/Numeric/.
-
-class FFTriangleTest : public ::testing::Test {
-};
-
-TEST_F(FFTriangleTest, Triangle)
-{
-    const double a = 1.;
-    const double as = a / 2;
-    const double ac = a / sqrt(3) / 2;
-    const double ah = a / sqrt(3);
-    const std::vector<R3> V{{-ac, as, 0.}, {-ac, -as, 0.}, {ah, 0., 0.}};
-
-    const PolyhedralFace T(V, false);
-    EXPECT_NEAR(T.area(), sqrt(3) / 4, 1e-15);
-
-    int failures = 0;
-    const int M = 37;
-    for (int j = 0; j < M; ++j) {
-        const double phi = M_PI_2 * j / (M - 1);
-        const C3 uQ{sin(phi), cos(phi), 0.};
-        const int N = 2800 + j;
-        for (int i = 0; i < N; ++i) {
-            const double q = 1e-17 * pow(1.7e17, i / (N - 1.));
-            const C3 Q = uQ * q;
-            const double f1 = std::abs(T.ff_2D_direct(Q));
-            const double f2 = std::abs(T.ff_2D_expanded(Q));
-            const double relerr = std::abs(f1 - f2) / f2;
-            if (relerr > 7e-16) {
-                printf("ERR1 %9.6f %16.11e %21.16e %21.16e %10.4e\n", phi, q, f1, f2, relerr);
-                ++failures;
-            }
-            if (q > 1e-7)
-                continue;
-            const double relerr2 = std::abs(f1 - T.area()) / f2;
-            if (relerr2 > 7e-16) {
-                printf("ERR2 %9.6f %16.11e %21.16e %21.16e %10.4e\n", phi, q, f1, f2, relerr2);
-                ++failures;
-            }
-        }
-    }
-    EXPECT_EQ(failures, 0);
-}