Could you put some more code inside the inner for loop so it could be looked at? I don't see problem with your loops being cleaver and faster but since you only access half the array index then your code has to do something like array[i][j]=array[j][i]=results maybe for collision and array[i][j]=-(array[j][i]=results) for attraction ; or else. It depends on what you have in the inner loop so list your code.

Giles has written a charged particle program with similar code. Look under programs board for charged particles.

Quote:

I don't believe you exactly... How did you create that array?

Maybe something like this: (warning: untested code)

Code:

int numX = 30;
int numY = 20;
Ball balls1d[] = new Ball[numY * numX];
Ball balls2d[][] = new Ball[numY][numX];

int i = 0; // 1D index

for (int y = 0; y < numY; y++)
{
  for (int x = 0; x < numX; x++)
  {
    // Create ONE ball object with TWO references
    balls2d[y][x] = balls1d[i] = new Ball();
    i++; // the 1d index for the next ball
  }
} 

Remember: the arrays only hold REFERENCES to the ball objects, and you can have as many references as you like to each object.

So, the above code (or some working version based on it) should allow you to access in two ways:

Code:

int x = 3; // column 4
int y = 5; // row 6
Ball theBall = balls2d[y][x];
Ball theSameBall = balls1d[y * numX + x]; // 5 * 30 + 3 = 153 

So, you can use balls1d the same was as you used to use the original array.

The real question, though, is why are you creating a 2D array in the first place? I'm supposing each ball bounces around independently, and its location has little to do with its 2D array indices.

-spxl

ok, i am sorry maybe i have to explain better what i am trying to do.
i am using traerphysics to create a mesh (10x10 matrix) of particles.
thats the reason why I use this 2d array because its ease to adress a single particle as "i" and "j" are his coodinates.

So when i played arround with traer physisc earlier and had some free floating particles stored in a 1d array and wanted every particle to have a attraction on every other particle i used these 2 for loops mentioned above.

What i now want to do is exactly the same. i have this mesh where every particle is connected to other ones by a spring. Now i want to create a negative attraction from any particle to any other particle. But dont want to repeat myself.

Hope its a bit clearer. Sorry for my vague explaination at first.