add new problem

1 files changed, 19 insertions, 0 deletions

diff --git a/buch/chapters/020-exponential/code/xxl.c b/buch/chapters/020-exponential/code/xxl.c
new file mode 100644
index 0000000..2c38ffe
--- /dev/null
+++ b/buch/chapters/020-exponential/code/xxl.c
@@ -0,0 +1,19 @@
+/*
+ * xxl.c -- find solution of x^x = 27
+ *
+ * (c) 2021 Prof Dr Andreas Müller, OST Ostschweizer Fachhochschue
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <gsl/gsl_sf_lambert.h>
+
+int	main(int argc, char *argv[]) {
+	double	b = 27;
+	double	w = gsl_sf_lambert_W0(log(b));
+	printf("W_0(log(27))  = %f\n", w);
+	double	x = exp(w);
+	printf("x             = %f\n", x);
+
+	return EXIT_SUCCESS;
+}