1 files changed, 126 insertions, 0 deletions
diff --git a/buch/chapters/110-elliptisch/images/lemnispara.cpp b/buch/chapters/110-elliptisch/images/lemnispara.cpp
new file mode 100644
index 0000000..6f4d55d
--- /dev/null
+++ b/buch/chapters/110-elliptisch/images/lemnispara.cpp
@@ -0,0 +1,126 @@
+/*
+ * lemnispara.cpp -- Display parametrisation of the lemniskate
+ *
+ * (c) 2022 Prof Dr Andreas Müller, OST Ostschweizer Fachhochschule
+ */
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
+#include <gsl/gsl_sf_elljac.h>
+#include <iostream>
+#include <fstream>
+#include <map>
+#include <string.h>
+#include <string>
+
+const static double	s = sqrt(2);
+const static double	k = 1 / s;
+const static double	m = k * k;
+
+typedef std::pair<double, double>	point_t;
+
+point_t	operator*(const point_t& p, double s) {
+	return point_t(s * p.first, s * p.second);
+}
+
+static double	norm(const point_t& p) {
+	return hypot(p.first, p.second);
+}
+
+static point_t	normalize(const point_t& p) {
+	return p * (1/norm(p));
+}
+
+static point_t	normal(const point_t& p) {
+	return std::make_pair(p.second, -p.first);
+}
+
+class lemniscate : public point_t {
+	double	sn, cn, dn;
+public:
+	lemniscate(double t) {
+		gsl_sf_elljac_e(t, m, &sn, &cn, &dn);
+		first = s * cn * dn;
+		second = cn * sn;
+	}
+	point_t	tangent() const {
+		return std::make_pair(-s * sn * (1.5 - sn * sn),
+				dn * (1 - 2 * sn * sn));
+	}
+	point_t	unittangent() const {
+		return normalize(tangent());
+	}
+	point_t	normal() const {
+		return ::normal(tangent());
+	}
+	point_t	unitnormal() const {
+		return ::normal(unittangent());
+	}
+};
+
+std::ostream&	operator<<(std::ostream& out, const point_t& p) {
+	char	b[1024];
+	snprintf(b, sizeof(b), "({%.4f*\\dx},{%.4f*\\dy})", p.first, p.second);
+	out << b;
+	return out;
+}
+
+int	main(int argc, char *argv[]) {
+	std::ofstream	out("lemnisparadata.tex");
+
+	// the curve
+	double	tstep = 0.01;
+	double tmax = 4.05;
+	out << "\\def\\lemnispath{ ";
+	out << lemniscate(0);
+	for (double t = tstep; t < tmax; t += tstep) {
+		out << std::endl << "\t" << "-- " << lemniscate(t);
+	}
+	out << std::endl;
+	out << "}" << std::endl;
+
+	out << "\\def\\lemnispathmore{ ";
+	out << lemniscate(tmax);
+	double	tmax2 = 7.5;
+	for (double t = tmax + tstep; t < tmax2; t += tstep) {
+		out << std::endl << "\t" << "-- " << lemniscate(t);
+	}
+	out << std::endl;
+	out << "}" << std::endl;
+
+	// individual points
+	tstep = 0.2;
+	int	i = 0;
+	char	name[3];
+	strcpy(name, "L0");
+	for (double t = 0; t <= tmax; t += tstep) {
+		char	c = 'A' + i++;
+		char	buffer[128];
+		lemniscate	l(t);
+		name[0] = 'L';
+		name[1] = c;
+		out << "\\coordinate (" << name << ") at ";
+		out << l << ";" << std::endl;
+		name[0] = 'T';
+		out << "\\coordinate (" << name << ") at ";
+		out << l.unittangent() << ";" << std::endl;
+		name[0] = 'N';
+		out << "\\coordinate (" << name << ") at ";
+		out << l.unitnormal() << ";" << std::endl;
+		name[0] = 'C';
+		out << "\\def\\" << name << "{ ";
+		out << "\\node[color=red] at ($(L" << c << ")+0.06*(N" << c << ")$) ";
+		out << "[rotate={";
+		double	w = 180 * atan2(l.unitnormal().second,
+					l.unitnormal().first) / M_PI;
+		snprintf(buffer, sizeof(buffer), "%.1f", w);
+		out << buffer;
+		out << "-90}]";
+		snprintf(buffer, sizeof(buffer), "%.1f", t);
+		out << " {$\\scriptstyle " << buffer << "$};" << std::endl;
+		out << "}" << std::endl;
+	}
+
+	out.close();
+	return EXIT_SUCCESS;
+}