The bug we address here is one encountered when (unfortunately) declaring a variable named datasize. Here is an small example.

    Let’s just include some simple 1D headers.

    #include "grid/multigrid1D.h"
    #include "run.h"

    We only put 4 points but this bug appears for more values of N, and in 2D as well.

    int main()
      N = 4;

    We setup a simple init event where we declare a variable named datasize as an integer and a scalar named toto.

    event init (i = 0) {
      int datasize = 7;
      scalar toto[];

    We fill toto with random values and display them in the same loop.

      printf ("Value of toto in the first loop :\n");
      foreach() {
        toto[] = noise();
        printf("%g ", toto[]);

    We display toto again, in another loop.

      printf ("\nValue of toto in the second loop :\n");
        printf("%g ", toto[]);

    We make it so the programm ends after only one time step, no need to go further to see the bug.

    event end (t = 0.00001) {
      printf ("\n");

    We get the following results :

    Value of toto in the first loop : -0.680375 0.211234 -0.566198 -0.59688

    Value of toto in the second loop : 6.92254e+235 -3.03422e-189 1.26266e+43 -0.59688

    The problem here is that when compiling (even with the -Wall -Wextra options), no error or warning is raised.

    Important note : This bug arises only when datasize < 8.