fix: pass **x instead

This is because when I pass *x then it's just a copy.

src/init.c

@@ -133,9 +133,9 @@ static void refine_interval(double xl, double xr, double yl, double yr, double r
   return ;
 }
 
-int init(double bmax, double rela_err_limit, int *size, double *x, double *y){
-  if (x) free(x);
-  if (y) free(y);
+int init(double bmax, double rela_err_limit, int *size, double **x, double **y){
+  if (*x) free(*x);
+  if (*y) free(*y);
   SampleData sample;
   sample.capacity = 1;
   sample.size=1;
@@ -155,12 +155,12 @@ int init(double bmax, double rela_err_limit, int *size, double *x, double *y){
   //printf("Total sample points capacity: %d\n", sample.capacity);
   //printf("Total sample points number: %d\n", sample.size);
   *size = sample.size;
-  x = malloc(sizeof(double) * sample.size);
-  y = malloc(sizeof(double) * sample.size);
+  *x = malloc(sizeof(double) * sample.size);
+  *y = malloc(sizeof(double) * sample.size);
   for (int i = 0; i < sample.size; i++) {
     //printf("%.16g %.16g\n", sample.x[i], sample.y[i]);
-    x[i] = sample.x[i];
-    y[i] = sample.y[i];
+    (*x)[i] = sample.x[i];
+    (*y)[i] = sample.y[i];
   }
 
   free(sample.x);