fix final main.c matutil.c matutil.h and add hw3.txt and README.md

hws/hw3/matutil.h

@@ -11,15 +11,24 @@ void print_vector_float(int size, float* v);
 void print_vector_int(int size, int* v);
 
 
-
 float **new_matrix(int m, int n);
 
+float **new_diagonal(int n, float *v);
+
 void print_matrix(int m, int n, float **mat);
 
 void copy_matrix(int m, int n, float **src, float **dst);
 
 void simple_free_matrix(int m, int n, float **mat);
 
+float **matmul(int m, int n, int p, float **a, float **b);
+
+float **mattranspose(int m, int n, float **mat);
+
+float **matinv(int m, float **mat);
+
+float matdet(int m, float **mat);
+
 /**
  * a struct for get solution of ax = b
  */