MASON actually has a MutableDouble.

	java/mason/sim/util/MutableDouble.java

You could use that.  Also, don't use for(Object object : objects) -- it translates to building an Iterator, and at least as of Java 7 Iterators are still quite slow.

I'd do this:

       final public void SparseGrid2DMultiply(SparseGrid2D theGrid, double multiplier) {
               Bag objects = theGrid.getAllObjects();
		int len = objects.size();
		for(int i = 0; i < len; i++)
			{
			MutableDouble d = (MutableDouble)(objects.get(i));
			d.val *= multiplier;
			}
		}


On Jun 15, 2015, at 1:02 PM, Sadat Chowdhury <[log in to unmask]> wrote:

> I still have a lot of files to change, and have not actually run/tested with this new method — maybe it would throw the  ConcurrentModificationException, I don’t know yet.
> 
> I am going to look into MutableDouble — it makes more sense as far as accuracy goes. Thanks!
> 
> 
>> On Jun 15, 2015, at 12:58 PM, Ernesto Carrella <[log in to unmask]> wrote:
>> 
>> 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 — 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 — I am at a point where I have a lot of DoubleGrid2D’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.