savefile and initfile

src/io.h

@@ -0,0 +1,12 @@
+#ifndef IO_H
+#define IO_H
+
+#include <stdio.h>
+
+// write u to file
+int write_u(_Complex double* u, int K1, int K2, FILE* file);
+
+// read u from file
+int read_u(_Complex double* u, int K1, int K2, FILE* file);
+
+#endif