# User:Devon McCormick/DLA/DiffLimAgg02

From J Wiki

Here's the penultimate version of our re-vamped DLA code as explained in some detail here.

NB.* DiffLimAgg02.ijs: diffusion-limited aggregation of random particles. NB. Adapted from http://www.jsoftware.com/jwiki/Studio/Gallery/DLA; NB. explained in the following sections as shown in "DLA_TOC" (following). DLA_TOC=: 0 : 0 (All the links following are rooted in the J wiki at http://www.jsoftware.com/jwiki/) The project starts here with an introduction to diffusion-limited aggregation and an implementation already on the J wiki: NYCJUG/2009-10-13#DLA.3AInitialJImplementation It continues here with a superficial re-vamp that aims to preserve how the original code works but make it superficially more J-like: DevonMcCormick/DLA00 We look at how this revised version performs by devising some performance metrics: DevonMcCormick/DLA0Runs Then we attempt a deeper re-vamp to make the code more J-like here: DevonMcCormick/DLA01 This section also makes use of the J profiler. We address a basic flaw in the original implementation here: DevonMcCormick/DLA00/BuildingACloseNeighborhood We explore the most crucial determinant of what shapes a DLA cluster by developing the "release policy" here: DevonMcCormick/DLA/SeekingRelease This also summarizes the basic, re-vamped code that works with an explicit, multi-dimensional list of points but releases only a single particle at a time. ) load 'coutil' cocurrent 'dla' NB. load 'mystats' load '~Code/math.ijs viewmat' init=: 3 : 0 D=: y NB. How many dimensions? RNI=: D dimnbr 1 NB. Relative neighbor indexes PTS=: ,:y$0 NB. List of points ) NB.EG init 2 NB. Initialize 2-dimensional space. NB.* aggStruc: make max rand walk y tries to aggregate point to structure, NB. (>0{x) away from random point in >1{x. aggStruc=: 4 : 0"(_ 0) point=. (>0{x) release >1{x [ ctr=. _1 while. y>ctr=. >:ctr do. point=. walk point if. PTS check_collision point do. y=. ctr [ addPt point end. end. ctr NB.EG (5;PTS) aggStruc 1e2$1e2 ) NB.* check_collision: 1 iff x in neighborhood of points y. check_collision=: 4 : '1 e. x e. RNI+"1 y' NB.* dimnbr: x-dimensional y-nearest neighbor offsets. dimnbr=: 13 : '(x$0)-.~,/>{x$<y-~i.>:+:y' NB. RNI=: (D$0)-.~(_1 0 1){~(D$3)#:i.3^D NB. Relative neighbor offsets NB.* addPt: add point to cluster, track indexes of points added. addPt=: 3 : 'PTS=: PTS,y' NB.* walk: walk one random step. walk=: 3 : 'y+RNI{~?#RNI' NB.* releaseIfOpen: release point x away from random point in y if NB. open (empty) neighborhood there. releaseIfOpen=: 4 : 0 while. 1 e. PTS e. RNI+"1 newpt=. ((]{~[:?#)y)+x*_1 1{~?D$2 do. end. newpt NB.EG dis releaseIfOpen PERIMPTS ) NB.* release: release new particle x away to find open neighborhood. release=: releaseIfOpen NB.* bordFill: fill 0-mat w/1 according to y, having border of x cells. bordFill=: 4 : '(1)(<"1 y-"1 x-~<./y)}0$~2$(>:+:x)+(>./y)-<./y' NB.EG viewmat 1 bordFill PTS neigh2=: 13 : 'x-.~~.,/y+"1/RNI' NB. Empty neighbors of these points. NB.EG PTS neigh2 PTS calcPerim=: 3 : 0 NP=: PTS neigh2^:(0{y)]PTS edges=. ~.PTS-.~NP -.~ ,/NP+"1/RNI edges=. ~.PTS neigh2^:(1{y)]edges NB.EG PPTS_dla_=: calcPerim 5 2 ) do1=: 3 : '(sv-~#PTS)%tm=. 6!:2 ''(2;PTS) aggStruc y'' [ sv=. #PTS' do1_dla_=: 4 : 0 if. 0=?10 do. PPTS=: calcPerim >1{x end. ((>0{x);PPTS) aggStruc y )