diff --git a/background.c b/background.c
index a73e662..28b4795 100644
--- a/background.c
+++ b/background.c
@@ -1,20 +1,10 @@
 #include <gsl/gsl_matrix_double.h>
 #include <stdint.h>
-#include <stdio.h>
-#include <gsl/gsl_errno.h>
 #include <gsl/gsl_odeiv2.h>
 #include <gsl/gsl_matrix.h>
-#include <math.h>
-#include <stdlib.h>
 #include <spng.h>
 
-#define PI 3.1415926535897932384626433832795028841971693993751058
-#define Rs 1
-#define M (0.5*Rs)
-#define R0 (15*Rs)
-#define f(r) ((1.0-Rs/((double)r)))
-#define bmin (1.5*sqrt(3.0))
-#define THETAERROR 100000
+#include "common.h"
 
 // ODE
 // du/dphi = v
diff --git a/common.h b/common.h
new file mode 100644
index 0000000..9298485
--- /dev/null
+++ b/common.h
@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <gsl/gsl_errno.h>
+
+#define PI 3.1415926535897932384626433832795028841971693993751058
+#define Rs 1
+#define M (0.5*Rs)
+#define R0 (15*Rs)
+#define f(r) ((1.0-Rs/((double)r)))
+#define bmin (1.5*sqrt(3.0))
+#define THETAERROR 100000
+