gsl-integ exercise

exercises/gsl-integ/Makefile

+CFLAGS = -Wall -Werror -O1
+CFLAGS += $(shell gsl-config --cflags)
+LDLIBS += $(shell gsl-config --libs)
+CC = gcc
+
+default: integral erf.gnuplot.png Makefile
+	./$<
+
+erf.gnuplot.png: erf_data.txt
+	echo '\
+	set terminal png;\
+	set output "$@";\
+	set key bottom right;\
+	set tics out;\
+	set xlabel "x";\
+	set ylabel "y";\
+	set title "Error function";\
+	set grid ytics xtics;\
+	show grid;\
+	plot\
+	"$<" using 1:2 with line title "Erf via integration",\
+	' | gnuplot
+
+erf_data.txt: erf
+	./$< > ./$@
+
+
+.PHONEY: clean
+clean:
+	$(RM) erf integral erf.gnuplot.png erf_data.txt
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exercises/gsl-integ/erf.c

+#include<stdio.h>
+#include<math.h>
+#include <gsl/gsl_integration.h>
+
+double integrand(double x, void* params) {
+	return exp(-pow(x,2));
+}
+
+double erf(double b) {
+	gsl_function F;
+	F.function = &integrand;
+	int limit = 9999;
+	gsl_integration_workspace* w;
+	w = gsl_integration_workspace_alloc(limit);
+	double a=0,acc=1e-6,eps=1e-6,result,error;
+	gsl_integration_qags(&F,a,b,acc,eps,limit,w,&result,&error);
+	gsl_integration_workspace_free(w);
+	return result;
+}
+
+int main() {
+	double xmin=-3,xmax=3,dx=1.0/1000;
+	for(double x=xmin;x<=xmax;x+=dx) {
+		printf("%10g%10g\n",x,erf(x));
+	}
+return 0;
+}
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exercises/gsl-integ/integral.c

+#include<stdio.h>
+#include<math.h>
+#include <gsl/gsl_integration.h>
+
+double my_f(double x, void* params) {
+	return log(x)/sqrt(x);
+}
+
+int main() {
+	gsl_function F;
+	F.function = &my_f;
+	int limit = 9999;
+	gsl_integration_workspace* w;
+	w = gsl_integration_workspace_alloc (limit);
+	double a=0,b=1,acc=1e-6,eps=1e-6,result,error;
+	gsl_integration_qags(&F,a,b,acc,eps,limit,w,&result,&error);
+	printf("Integralet giver: %g med fejl %g\n",result,error);
+	gsl_integration_workspace_free(w);
+return 0;
+}
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