RE: [Repast-interest] Question for Conway's Life Project

[Nick C. <nic...@ve...>]

Hendy,

The idea here, I think, is that the space in which the life CA's operate is
a sparse matrix. This sparse matrix is backed by a hashtable. If we want to
use integer indexes to the hastable then we need to insure that the indexes
are with the limits of an int. The sqrt gives us the row / col dimensions of
a matrix and the -1 is for saftey in case of any rounding irregularities.
This way we can be sure that if we multiply the largest row index by the
largest col index we get a valid int.

The int index ... line below calculates the key into the sparse matrix.

Nick
  -----Original Message-----
  From: rep...@li...
[mailto:rep...@li...]On Behalf Of Hendy
Gunawan
  Sent: Wednesday, October 27, 2004 7:38 AM
  To: RePast
  Subject: [Repast-interest] Question for Conway's Life Project


  Hi RePast community,



  I am a new member in RePast member.

  I'm studying in TU Delft and new to agent based modeling.

  I try RePast and look at the codes of the demos and actually, I like it.

  I'm also quite new in Java programming and usually using Dsol (another
free simulation language from Sourceforge).



  I have questions regarding the reason(s) behind several programming line
from Life demo project.

  In class InfiniteLifeSpace:



  public static final int MAX = (int)Math.sqrt(Integer.MAX_VALUE) - 1;



  Is there any specific reason why the programmer used sqrt method and -1
for example?



  for (int j = y - yTop; j <= y + yBottom; j++) {

              for (int i = x - xLeft; i <= x + xRight; i++) {

                if (!(j == y && i == x)) {

                  int index = j * MAX + i;

                  if (!checkedSpace.containsKey(index)) {

                    if (isEmptyAt(i, j) && getNumNeighbors(i, j) == 3) {

                          model.addAgent(new LifeAgent(i, j, this));

                          checkedSpace.put(index, dummy);



  I cannot figure out the reasons behind the above bolded lines.



  I appreciate any help or comments even partlyJ



  Best regards,

  Hendy Gunawan