buffer = (double*) malloc((r + r + r) * sizeof(double *) +
    (r*r + r*r + r*r) * sizeof(double));

  if(buffer == NULL) {
    printf("out of memoryn");
    return 0;
  }

  for(i = 0, j = 0; i < r; i++) {
    a[i] = &buffer[j];
    j+=r;
  }

  for(i = 0; i < r; i++) {
    b[i] = &buffer[j];
    j+=r;
  }

  for(i = 0; i < r; i++) {
    c[i] = &buffer[j];
    j+=r;
  }

  a = buffer[j];
  b = buffer[j + r];
  c = buffer[j + r + r];

double* all = (double*) malloc( 3*r*r*sizeof(double));

double *p1 = all;
double *p2 = &all[r*r];
double *p3 = &all[2*r*r];

size_t r = ...;

double (*a)[r] = NULL;
double (*b)[r] = NULL;
double (*c)[r] = NULL;

double (*backing_store)[r][r] = malloc(3 * sizeof *backing_store);
if (!backing_store)
{
  // panic and exit
}

a = backing_store[0];
b = backing_store[1];
c = backing_store[2];

a[i][j] = ...;
printf("%fn", b[x][y]);

free(backing_store);

#define R ...

double (*a)[R] = NULL;
double (*b)[R] = NULL;
double (*c)[R] = NULL;

double (*backing_store)[R][R] = malloc(3 * sizeof *backing_store);
if (!backing_store)
{
  // panic and exit
}

a = backing_store[0];
b = backing_store[1];
c = backing_store[2];

double *a = NULL;
double *b = NULL;
double *c = NULL;

double *backing_store = malloc(3 * r * r * sizeof *backing_store);
if (!backing_store)
{
  // panic
}

a = backing_store;
b = backing_store + r * r;
c = backing_store + 2 * r * r;

a[i*r+j] = ...;
printf("%fn", b[x*r+y]);

free(backing_store);

double (*Memory)[r][r] = malloc(3 * sizeof *Memory);
    // Now Memory points to three r-by-r arrays of double.
double (*a)[r] = Memory[0];
double (*b)[r] = Memory[1];
double (*c)[r] = Memory[2];

double *(*PointerMemory)[r] = malloc(3 * sizeof *PointerMemory);
    // PointerMemory points to three arrays of r elements of pointers to double.
double (*ElementMemory)[r][r] = malloc(3 * sizeof *ElementMemory);

// Set a to point to the first array of r elements of pointers to double.
double *a[r] = PointerMemory[0];
// Initialize the elements of a to point to rows of the first r-by-r array of double.
for (i = 0; i < r; ++i)
    a[i] = ElementMemory[0][i];

// Set b for the second array of pointers and the second array of double.
double *b[r] = PointerMemory[0];
for (i = 0; i < r; ++i)
    b[i] = ElementMemory[1][i];

// Set c for the third arrays.
double *c[r] = PointerMemory[0];
for (i = 0; i < r; ++i)
    c[i] = ElementMemory[2][i];