You could try populating your SparseGrid2D with either an AtomicDouble or a
MutableDouble from commons-lang.
That way you can modify them without pulling them out of the grid and
putting them back in.

I am quite surprised it doesn't throw a ConcurrentModification exception
since you are effectively looping through a list of objects that you are
also modifying (with remove() and setLocation()). I suppose MASON passes a
safe copy in that bag.

On Mon, Jun 15, 2015 at 5:23 PM Sadat Chowdhury <[log in to unmask]> wrote:

> Hi All,
> When I increased the 2D world size of my system, there was a significant
> slowdown of the simulation. After I investigated using a profiler, it
> turned out to be due to methods that scan through 2D grids that in my
> system are defined as DoubleGrid2D.
> I have started converting those DoubleGrid2D into SparseGrid2D ā€” because
> it fits the description perfectly: the world can be potentially unbounded
> and most times there will be fewer actual objects in the world.
> While it was relatively easy to convert all the parts that was setting and
> accessing objects in the grid ā€” I am at a point where I have a lot of
> DoubleGrid2Dā€™s that used full-scanning functions like .lowerBound() and
> .multiply(). Supposing I have a SparseGrid2D that has only one Double
> object per coordinate, what would be the most efficient (fast) way to
> implement a function similar to multiply() ?
> This is what I have so far, but I am just wondering if it can be done more
> efficiently (faster)?
>         final public void SparseGrid2DMultiply(SparseGrid2D theGrid,
>                         double multiplier) {
>                 /*
>                  * theGrid is assumed to contain one and only one Double
> in a given
>                  * coordinate
>                  */
>                 Bag objects = theGrid.getAllObjects();
>                 for (Object object : objects) {
>                         double val = (Double) object;
>                         if (val != 0.0) {
>                                 val = val * multiplier;
>                                 Int2D location =
> theGrid.getObjectLocation(object);
>                                 theGrid.remove(object);
>                                 theGrid.setObjectLocation(val, location);
>                         }
>                 }
>         }
> Any thoughts/comments is greatly appreciated,
> Sadat.