From 409777bc146b139ac2ddbf0cd6564275fd20928c Mon Sep 17 00:00:00 2001
From: Pitchaya Boonsarngsuk <2285135b@student.gla.ac.uk>
Date: Tue, 30 Jan 2018 20:10:46 +0000
Subject: [PATCH] Link: optimize so that no link {} is used, less than half the
 ram used

---
 .../linkForce.js                              | 34 +++++++++++--------
 src/link.js                                   | 17 +++++-----
 2 files changed, 29 insertions(+), 22 deletions(-)

diff --git a/examples/js/src/neighbourSampling-papaparsing/linkForce.js b/examples/js/src/neighbourSampling-papaparsing/linkForce.js
index 681164c..cf35e17 100644
--- a/examples/js/src/neighbourSampling-papaparsing/linkForce.js
+++ b/examples/js/src/neighbourSampling-papaparsing/linkForce.js
@@ -8,17 +8,28 @@ function startLinkSimulation() {
   manualStop = true;
   simulation.stop();
   p1 = performance.now();
-  let links = [];
+  let links = [], force;
 
-  // Initialize link array.
-  nodes = simulation.nodes();
-  for (i = nodes.length-1; i >= 1; i--) {
-    for (j = i-1; j >= 0; j--) {
-      links.push({
-        source: nodes[i],
-        target: nodes[j],
-      });
+  if (tweakedVerOfLink) {
+    force = d3.forceLinkTweaked()
+              .distance(function (n) {
+                return distanceFunction(n.source, n.target, props, norm);
+              });
+  }
+  else {
+    for (i = nodes.length-1; i >= 1; i--) {
+      for (j = i-1; j >= 0; j--) {
+        links.push({
+          source: nodes[i],
+          target: nodes[j],
+        });
+      }
     }
+    force = d3.forceLink()
+              .distance(function (n) {
+               return distanceFunction(n.source, n.target, props, norm);
+              })
+             .links(links);
   }
 
   /* Add force
@@ -33,11 +44,6 @@ function startLinkSimulation() {
    * The full pre-calculation will then occur once when the force is being
    *   initialized by the simulation.
    */
-  let force = tweakedVerOfLink ? d3.forceLinkTweaked() : d3.forceLink();
-  force.distance(function (n) {
-         return distanceFunction(n.source, n.target, props, norm);
-        })
-       .links(links);
 
   simulation
     .alphaDecay(0)
diff --git a/src/link.js b/src/link.js
index 537ea1b..8037180 100644
--- a/src/link.js
+++ b/src/link.js
@@ -18,17 +18,16 @@ export default function(links) {
 
   function force(alpha) {
     // Each iteration in a tick
-    for (var k = 0, n = links.length; k < iterations; ++k) {
+    for (var k = 0, n = nodes.length, source, target, i, j, x, y, l; k < iterations; ++k) {
       // For each link
-      for (var i = 0, link, source, target, x, y, l, b; i < n; ++i) {
-        link = links[i];
+      for (i = 1; i < n; i++) for (j = 0; j < i; j++) {
         // jiggle so it wont divide / multiply by zero after this
-        source = link.source;
-        target = link.target;
+        source = nodes[i];
+        target = nodes[j];
         x = target.x + target.vx - source.x - source.vx || jiggle();
         y = target.y + target.vy - source.y - source.vy || jiggle();
         l = Math.sqrt(x * x + y * y);
-        l = (l - distances[i]) / l  * dataSizeFactor * alpha;
+        l = (l - distances[i*(i-1)/2+j]) / l  * dataSizeFactor * alpha;
         x *= l, y *= l;
         target.vx -= x;
         target.vy -= y;
@@ -46,8 +45,10 @@ export default function(links) {
 
   function initializeDistance() {
     if (!nodes) return;
-    for (var i = 0, n = links.length; i < n; ++i) {
-      distances[i] = +distance(links[i], i, links);
+    for (let i = 1, n = nodes.length; i < n; i++) {
+      for (let j = 0; j < i; j++) {
+        distances.push(distanceFunction(nodes[i], nodes[j], props, norm));
+      }
     }
   }