diff --git a/lib/arbor.js b/lib/arbor.js
index 15ebf82..108de47 100644
--- a/lib/arbor.js
+++ b/lib/arbor.js
@@ -32,7 +32,7 @@
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-  /*     system.js */  var ParticleSystem=function(d,p,e,f,t,l,q){var j=[];var h=null;var k=0;var u=null;var m=0.04;var i=[20,20,20,20];var n=null;var o=null;if(typeof p=="object"){var s=p;e=s.friction;d=s.repulsion;t=s.fps;l=s.dt;p=s.stiffness;f=s.gravity;q=s.precision}e=isNaN(e)?0.5:e;d=isNaN(d)?1000:d;t=isNaN(t)?55:t;p=isNaN(p)?600:p;l=isNaN(l)?0.02:l;q=isNaN(q)?0.6:q;f=(f===true);var r=(t!==undefined)?1000/t:1000/50;var b={repulsion:d,stiffness:p,friction:e,dt:l,gravity:f,precision:q,timeout:r};var a;var c={renderer:null,tween:null,nodes:{},edges:{},adjacency:{},names:{},kernel:null};var g={parameters:function(v){if(v!==undefined){if(!isNaN(v.precision)){v.precision=Math.max(0,Math.min(1,v.precision))}$.each(b,function(x,w){if(v[x]!==undefined){b[x]=v[x]}});c.kernel.physicsModified(v)}return b},fps:function(v){if(v===undefined){return 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w=g.getNode(y);if(w){c.tween.to(w,v,x)}},tweenEdge:function(w,v,z,y){if(y===undefined){g._tweenEdge(w,v,z)}else{var x=g.getEdges(w,v);$.each(x,function(A,B){g._tweenEdge(B,z,y)})}},_tweenEdge:function(w,v,x){if(w&&w._id!==undefined){c.tween.to(w,v,x)}},_updateGeometry:function(y){if(y!=undefined){var v=(y.epoch<k);a=y.energy;var z=y.geometry;if(z!==undefined){for(var x=0,w=z.length/3;x<w;x++){var A=z[3*x];if(v&&c.nodes[A]==undefined){continue}c.nodes[A]._p.x=z[3*x+1];c.nodes[A]._p.y=z[3*x+2]}}}},screen:function(v){if(v.size!==undefined){g.screenSize(v.size.width,v.size.height)}if(!isNaN(v.step)){g.screenStep(v.step)}if(v.padding!==undefined){g.screenPadding(v.padding)}},screenSize:function(v,w){u={width:v,height:w};g._updateBounds()},screenPadding:function(y,z,v,w){if($.isArray(y)){trbl=y}else{trbl=[y,z,v,w]}var A=trbl[0];var x=trbl[1];var B=trbl[2];if(x===undefined){trbl=[A,A,A,A]}else{if(B==undefined){trbl=[A,x,A,x]}}i=trbl},screenStep:function(v){m=v},toScreen:function(x){if(!n||!u){return}var w=i||[0,0,0,0];var v=n.bottomright.subtract(n.topleft);var z=w[3]+x.subtract(n.topleft).divide(v.x).x*(u.width-(w[1]+w[3]));var y=w[0]+x.subtract(n.topleft).divide(v.y).y*(u.height-(w[0]+w[2]));return arbor.Point(z,y)},fromScreen:function(z){if(!n||!u){return}var y=i||[0,0,0,0];var x=n.bottomright.subtract(n.topleft);var w=(z.x-y[3])/(u.width-(y[1]+y[3]))*x.x+n.topleft.x;var v=(z.y-y[0])/(u.height-(y[0]+y[2]))*x.y+n.topleft.y;return arbor.Point(w,v)},_updateBounds:function(w){if(u===null){return}if(w){o=w}else{o=g.bounds()}var z=new Point(o.bottomright.x,o.bottomright.y);var y=new Point(o.topleft.x,o.topleft.y);var B=z.subtract(y);var v=y.add(B.divide(2));var x=4;var D=new Point(Math.max(B.x,x),Math.max(B.y,x));o.topleft=v.subtract(D.divide(2));o.bottomright=v.add(D.divide(2));if(!n){if($.isEmptyObject(c.nodes)){return false}n=o;return true}var C=m;_newBounds={bottomright:n.bottomright.add(o.bottomright.subtract(n.bottomright).multiply(C)),topleft:n.topleft.add(o.topleft.subtract(n.topleft).multiply(C))};var A=new Point(n.topleft.subtract(_newBounds.topleft).magnitude(),n.bottomright.subtract(_newBounds.bottomright).magnitude());if(A.x*u.width>1||A.y*u.height>1){n=_newBounds;return true}else{return false}},energy:function(){return a},bounds:function(){var w=null;var v=null;$.each(c.nodes,function(z,y){if(!w){w=new Point(y._p);v=new Point(y._p);return}var x=y._p;if(x.x===null||x.y===null){return}if(x.x>w.x){w.x=x.x}if(x.y>w.y){w.y=x.y}if(x.x<v.x){v.x=x.x}if(x.y<v.y){v.y=x.y}});if(w&&v){return{bottomright:w,topleft:v}}else{return{topleft:new Point(-1,-1),bottomright:new Point(1,1)}}},nearest:function(x){if(u!==null){x=g.fromScreen(x)}var w={node:null,point:null,distance:null};var v=g;$.each(c.nodes,function(B,y){var z=y._p;if(z.x===null||z.y===null){return}var A=z.subtract(x).magnitude();if(w.distance===null||A<w.distance){w={node:y,point:z,distance:A};if(u!==null){w.screenPoint=g.toScreen(z)}}});if(w.node){if(u!==null){w.distance=g.toScreen(w.node.p).subtract(g.toScreen(x)).magnitude()}return w}else{return null}},_notify:function(){if(h===null){k++}else{clearTimeout(h)}h=setTimeout(g._synchronize,20)},_synchronize:function(){if(j.length>0){c.kernel.graphChanged(j);j=[];h=null}},};c.kernel=Kernel(g);c.tween=c.kernel.tween||null;Node.prototype.__defineGetter__("p",function(){var w=this;var v={};v.__defineGetter__("x",function(){return w._p.x});v.__defineSetter__("x",function(x){c.kernel.particleModified(w._id,{x:x})});v.__defineGetter__("y",function(){return w._p.y});v.__defineSetter__("y",function(x){c.kernel.particleModified(w._id,{y:x})});v.__proto__=Point.prototype;return 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+  /*     system.js */  var ParticleSystem=function(d,p,e,f,t,l,q){var j=[];var h=null;var k=0;var u=null;var m=0.04;var i=[20,20,20,20];var n=null;var o=null;if(typeof p=="object"){var s=p;e=s.friction;d=s.repulsion;t=s.fps;l=s.dt;p=s.stiffness;f=s.gravity;q=s.precision}e=isNaN(e)?0.5:e;d=isNaN(d)?1000:d;t=isNaN(t)?55:t;p=isNaN(p)?600:p;l=isNaN(l)?0.02:l;q=isNaN(q)?0.6:q;f=(f===true);var r=(t!==undefined)?1000/t:1000/50;var b={repulsion:d,stiffness:p,friction:e,dt:l,gravity:f,precision:q,timeout:r};var a;var c={renderer:null,tween:null,nodes:{},edges:{},adjacency:{},names:{},kernel:null};var g={parameters:function(v){if(v!==undefined){if(!isNaN(v.precision)){v.precision=Math.max(0,Math.min(1,v.precision))}$.each(b,function(x,w){if(v[x]!==undefined){b[x]=v[x]}});c.kernel.physicsModified(v)}return b},fps:function(v){if(v===undefined){return c.kernel.fps()}else{g.parameters({timeout:1000/(v||50)})}},start:function(){c.kernel.start()},stop:function(){c.kernel.stop()},addNode:function(w,B){B=B||{};var C=c.names[w];if(C){C.data=B;return C}else{if(w!=undefined){var v=(B.x!=undefined)?B.x:null;var D=(B.y!=undefined)?B.y:null;var A=(B.fixed)?1:0;var z=new Node(B);z.name=w;c.names[w]=z;c.nodes[z._id]=z;j.push({t:"addNode",id:z._id,m:z.mass,x:v,y:D,f:A});g._notify();return z}}},pruneNode:function(w){var v=g.getNode(w);if(typeof(c.nodes[v._id])!=="undefined"){delete c.nodes[v._id];delete c.names[v.name]}$.each(c.edges,function(y,x){if(x.source._id===v._id||x.target._id===v._id){g.pruneEdge(x)}});j.push({t:"dropNode",id:v._id});g._notify()},getNode:function(v){if(v._id!==undefined){return v}else{if(typeof v=="string"||typeof v=="number"){return c.names[v]}}},eachNode:function(v){$.each(c.nodes,function(y,x){if(x._p.x==null||x._p.y==null){return}var w=(u!==null)?g.toScreen(x._p):x._p;v.call(g,x,w)})},addEdge:function(z,A,y){z=g.getNode(z)||g.addNode(z);A=g.getNode(A)||g.addNode(A);y=y||{};var x=new Edge(z,A,y);var B=z._id;var C=A._id;c.adjacency[B]=c.adjacency[B]||{};c.adjacency[B][C]=c.adjacency[B][C]||[];var w=(c.adjacency[B][C].length>0);if(w){$.extend(c.adjacency[B][C].data,x.data);return}else{c.edges[x._id]=x;c.adjacency[B][C].push(x);var v=(x.length!==undefined)?x.length:1;j.push({t:"addSpring",id:x._id,fm:B,to:C,l:v});g._notify()}return x},pruneEdge:function(A){j.push({t:"dropSpring",id:A._id});delete c.edges[A._id];for(var v in c.adjacency){for(var B in c.adjacency[v]){var w=c.adjacency[v][B];for(var z=w.length-1;z>=0;z--){if(c.adjacency[v][B][z]._id===A._id){c.adjacency[v][B].splice(z,1)}}}}g._notify()},getEdges:function(w,v){w=g.getNode(w);v=g.getNode(v);if(!w||!v){return[]}if(typeof(c.adjacency[w._id])!=="undefined"&&typeof(c.adjacency[w._id][v._id])!=="undefined"){return c.adjacency[w._id][v._id]}return[]},getEdgesFrom:function(v){v=g.getNode(v);if(!v){return[]}if(typeof(c.adjacency[v._id])!=="undefined"){var w=[];$.each(c.adjacency[v._id],function(y,x){w=w.concat(x)});return w}return[]},getEdgesTo:function(v){v=g.getNode(v);if(!v){return[]}var w=[];$.each(c.edges,function(y,x){if(x.target==v){w.push(x)}});return w},eachEdge:function(v){$.each(c.edges,function(z,x){var y=c.nodes[x.source._id]._p;var w=c.nodes[x.target._id]._p;if(y.x==null||w.x==null){return}y=(u!==null)?g.toScreen(y):y;w=(u!==null)?g.toScreen(w):w;if(y&&w){v.call(g,x,y,w)}})},prune:function(w){var v={dropped:{nodes:[],edges:[]}};if(w===undefined){$.each(c.nodes,function(y,x){v.dropped.nodes.push(x);g.pruneNode(x)})}else{g.eachNode(function(y){var x=w.call(g,y,{from:g.getEdgesFrom(y),to:g.getEdgesTo(y)});if(x){v.dropped.nodes.push(y);g.pruneNode(y)}})}return v},graft:function(w){var v={added:{nodes:[],edges:[]}};if(w.nodes){$.each(w.nodes,function(y,x){var z=g.getNode(y);if(z){z.data=x}else{v.added.nodes.push(g.addNode(y,x))}c.kernel.start()})}if(w.edges){$.each(w.edges,function(z,x){var y=g.getNode(z);if(!y){v.added.nodes.push(g.addNode(z,{}))}$.each(x,function(D,A){var C=g.getNode(D);if(!C){v.added.nodes.push(g.addNode(D,{}))}var B=g.getEdges(z,D);if(B.length>0){B[0].data=A}else{v.added.edges.push(g.addEdge(z,D,A))}})})}return v},merge:function(w){var v={added:{nodes:[],edges:[]},dropped:{nodes:[],edges:[]}};$.each(c.edges,function(A,z){if((w.edges[z.source.name]===undefined||w.edges[z.source.name][z.target.name]===undefined)){g.pruneEdge(z);v.dropped.edges.push(z)}});var y=g.prune(function(A,z){if(w.nodes[A.name]===undefined){v.dropped.nodes.push(A);return true}});var x=g.graft(w);v.added.nodes=v.added.nodes.concat(x.added.nodes);v.added.edges=v.added.edges.concat(x.added.edges);v.dropped.nodes=v.dropped.nodes.concat(y.dropped.nodes);v.dropped.edges=v.dropped.edges.concat(y.dropped.edges);return v},tweenNode:function(y,v,x){var w=g.getNode(y);if(w){c.tween.to(w,v,x)}},tweenEdge:function(w,v,z,y){if(y===undefined){g._tweenEdge(w,v,z)}else{var x=g.getEdges(w,v);$.each(x,function(A,B){g._tweenEdge(B,z,y)})}},_tweenEdge:function(w,v,x){if(w&&w._id!==undefined){c.tween.to(w,v,x)}},_updateGeometry:function(y){if(y!=undefined){var v=(y.epoch<k);a=y.energy;var z=y.geometry;if(z!==undefined){for(var x=0,w=z.length/3;x<w;x++){var A=z[3*x];if(v&&c.nodes[A]==undefined){continue}c.nodes[A]._p.x=z[3*x+1];c.nodes[A]._p.y=z[3*x+2]}}}},screen:function(v){if(v==undefined){return{size:(u)?objcopy(u):undefined,padding:i.concat(),step:m}}if(v.size!==undefined){g.screenSize(v.size.width,v.size.height)}if(!isNaN(v.step)){g.screenStep(v.step)}if(v.padding!==undefined){g.screenPadding(v.padding)}},screenSize:function(v,w){u={width:v,height:w};g._updateBounds()},screenPadding:function(y,z,v,w){if($.isArray(y)){trbl=y}else{trbl=[y,z,v,w]}var A=trbl[0];var x=trbl[1];var B=trbl[2];if(x===undefined){trbl=[A,A,A,A]}else{if(B==undefined){trbl=[A,x,A,x]}}i=trbl},screenStep:function(v){m=v},toScreen:function(x){if(!n||!u){return}var w=i||[0,0,0,0];var v=n.bottomright.subtract(n.topleft);var z=w[3]+x.subtract(n.topleft).divide(v.x).x*(u.width-(w[1]+w[3]));var y=w[0]+x.subtract(n.topleft).divide(v.y).y*(u.height-(w[0]+w[2]));return arbor.Point(z,y)},fromScreen:function(z){if(!n||!u){return}var y=i||[0,0,0,0];var x=n.bottomright.subtract(n.topleft);var w=(z.x-y[3])/(u.width-(y[1]+y[3]))*x.x+n.topleft.x;var v=(z.y-y[0])/(u.height-(y[0]+y[2]))*x.y+n.topleft.y;return arbor.Point(w,v)},_updateBounds:function(w){if(u===null){return}if(w){o=w}else{o=g.bounds()}var z=new Point(o.bottomright.x,o.bottomright.y);var y=new Point(o.topleft.x,o.topleft.y);var B=z.subtract(y);var v=y.add(B.divide(2));var x=4;var D=new Point(Math.max(B.x,x),Math.max(B.y,x));o.topleft=v.subtract(D.divide(2));o.bottomright=v.add(D.divide(2));if(!n){if($.isEmptyObject(c.nodes)){return false}n=o;return true}var C=m;_newBounds={bottomright:n.bottomright.add(o.bottomright.subtract(n.bottomright).multiply(C)),topleft:n.topleft.add(o.topleft.subtract(n.topleft).multiply(C))};var A=new Point(n.topleft.subtract(_newBounds.topleft).magnitude(),n.bottomright.subtract(_newBounds.bottomright).magnitude());if(A.x*u.width>1||A.y*u.height>1){n=_newBounds;return true}else{return false}},energy:function(){return a},bounds:function(){var w=null;var v=null;$.each(c.nodes,function(z,y){if(!w){w=new Point(y._p);v=new Point(y._p);return}var x=y._p;if(x.x===null||x.y===null){return}if(x.x>w.x){w.x=x.x}if(x.y>w.y){w.y=x.y}if(x.x<v.x){v.x=x.x}if(x.y<v.y){v.y=x.y}});if(w&&v){return{bottomright:w,topleft:v}}else{return{topleft:new Point(-1,-1),bottomright:new Point(1,1)}}},nearest:function(x){if(u!==null){x=g.fromScreen(x)}var w={node:null,point:null,distance:null};var v=g;$.each(c.nodes,function(B,y){var z=y._p;if(z.x===null||z.y===null){return}var A=z.subtract(x).magnitude();if(w.distance===null||A<w.distance){w={node:y,point:z,distance:A};if(u!==null){w.screenPoint=g.toScreen(z)}}});if(w.node){if(u!==null){w.distance=g.toScreen(w.node.p).subtract(g.toScreen(x)).magnitude()}return w}else{return null}},_notify:function(){if(h===null){k++}else{clearTimeout(h)}h=setTimeout(g._synchronize,20)},_synchronize:function(){if(j.length>0){c.kernel.graphChanged(j);j=[];h=null}},};c.kernel=Kernel(g);c.tween=c.kernel.tween||null;Node.prototype.__defineGetter__("p",function(){var w=this;var v={};v.__defineGetter__("x",function(){return w._p.x});v.__defineSetter__("x",function(x){c.kernel.particleModified(w._id,{x:x})});v.__defineGetter__("y",function(){return w._p.y});v.__defineSetter__("y",function(x){c.kernel.particleModified(w._id,{y:x})});v.__proto__=Point.prototype;return v});Node.prototype.__defineSetter__("p",function(v){this._p.x=v.x;this._p.y=v.y;c.kernel.particleModified(this._id,{x:v.x,y:v.y})});Node.prototype.__defineGetter__("mass",function(){return this._mass});Node.prototype.__defineSetter__("mass",function(v){this._mass=v;c.kernel.particleModified(this._id,{m:v})});Node.prototype.__defineSetter__("tempMass",function(v){c.kernel.particleModified(this._id,{_m:v})});Node.prototype.__defineGetter__("fixed",function(){return this._fixed});Node.prototype.__defineSetter__("fixed",function(v){this._fixed=v;c.kernel.particleModified(this._id,{f:v?1:0})});return g};
   /* barnes-hut.js */  var BarnesHutTree=function(){var b=[];var a=0;var e=null;var d=0.5;var c={init:function(g,h,f){d=f;a=0;e=c._newBranch();e.origin=g;e.size=h.subtract(g)},insert:function(j){var f=e;var g=[j];while(g.length){var h=g.shift();var m=h._m||h.m;var p=c._whichQuad(h,f);if(f[p]===undefined){f[p]=h;f.mass+=m;if(f.p){f.p=f.p.add(h.p.multiply(m))}else{f.p=h.p.multiply(m)}}else{if("origin" in f[p]){f.mass+=(m);if(f.p){f.p=f.p.add(h.p.multiply(m))}else{f.p=h.p.multiply(m)}f=f[p];g.unshift(h)}else{var l=f.size.divide(2);var n=new Point(f.origin);if(p[0]=="s"){n.y+=l.y}if(p[1]=="e"){n.x+=l.x}var o=f[p];f[p]=c._newBranch();f[p].origin=n;f[p].size=l;f.mass=m;f.p=h.p.multiply(m);f=f[p];if(o.p.x===h.p.x&&o.p.y===h.p.y){var k=l.x*0.08;var i=l.y*0.08;o.p.x=Math.min(n.x+l.x,Math.max(n.x,o.p.x-k/2+Math.random()*k));o.p.y=Math.min(n.y+l.y,Math.max(n.y,o.p.y-i/2+Math.random()*i))}g.push(o);g.unshift(h)}}}},applyForces:function(m,g){var f=[e];while(f.length){node=f.shift();if(node===undefined){continue}if(m===node){continue}if("f" in node){var k=m.p.subtract(node.p);var l=Math.max(1,k.magnitude());var i=((k.magnitude()>0)?k:Point.random(1)).normalize();m.applyForce(i.multiply(g*(node._m||node.m)).divide(l*l))}else{var j=m.p.subtract(node.p.divide(node.mass)).magnitude();var h=Math.sqrt(node.size.x*node.size.y);if(h/j>d){f.push(node.ne);f.push(node.nw);f.push(node.se);f.push(node.sw)}else{var k=m.p.subtract(node.p.divide(node.mass));var l=Math.max(1,k.magnitude());var i=((k.magnitude()>0)?k:Point.random(1)).normalize();m.applyForce(i.multiply(g*(node.mass)).divide(l*l))}}}},_whichQuad:function(i,f){if(i.p.exploded()){return null}var h=i.p.subtract(f.origin);var g=f.size.divide(2);if(h.y<g.y){if(h.x<g.x){return"nw"}else{return"ne"}}else{if(h.x<g.x){return"sw"}else{return"se"}}},_newBranch:function(){if(b[a]){var f=b[a];f.ne=f.nw=f.se=f.sw=undefined;f.mass=0;delete f.p}else{f={origin:null,size:null,nw:undefined,ne:undefined,sw:undefined,se:undefined,mass:0};b[a]=f}a++;return f}};return c};
   /*    physics.js */  var Physics=function(a,m,n,e,h){var f=BarnesHutTree();var c={particles:{},springs:{}};var l={particles:{}};var o=[];var k=[];var d=0;var b={sum:0,max:0,mean:0};var g={topleft:new Point(-1,-1),bottomright:new Point(1,1)};var j=1000;var i={stiffness:(m!==undefined)?m:1000,repulsion:(n!==undefined)?n:600,friction:(e!==undefined)?e:0.3,gravity:false,dt:(a!==undefined)?a:0.02,theta:0.4,init:function(){return i},modifyPhysics:function(p){$.each(["stiffness","repulsion","friction","gravity","dt","precision"],function(r,s){if(p[s]!==undefined){if(s=="precision"){i.theta=1-p[s];return}i[s]=p[s];if(s=="stiffness"){var q=p[s];$.each(c.springs,function(u,t){t.k=q})}}})},addNode:function(u){var t=u.id;var q=u.m;var p=g.bottomright.x-g.topleft.x;var s=g.bottomright.y-g.topleft.y;var r=new Point((u.x!=null)?u.x:g.topleft.x+p*Math.random(),(u.y!=null)?u.y:g.topleft.y+s*Math.random());c.particles[t]=new Particle(r,q);c.particles[t].connections=0;c.particles[t].fixed=(u.f===1);l.particles[t]=c.particles[t];o.push(c.particles[t])},dropNode:function(s){var r=s.id;var q=c.particles[r];var p=$.inArray(q,o);if(p>-1){o.splice(p,1)}delete c.particles[r];delete l.particles[r]},modifyNode:function(r,p){if(r in c.particles){var q=c.particles[r];if("x" in p){q.p.x=p.x}if("y" in p){q.p.y=p.y}if("m" in p){q.m=p.m}if("f" in p){q.fixed=(p.f===1)}if("_m" in p){if(q._m===undefined){q._m=q.m}q.m=p._m}}},addSpring:function(t){var s=t.id;var p=t.l;var r=c.particles[t.fm];var q=c.particles[t.to];if(r!==undefined&&q!==undefined){c.springs[s]=new Spring(r,q,p,i.stiffness);k.push(c.springs[s]);r.connections++;q.connections++;delete l.particles[t.fm];delete l.particles[t.to]}},dropSpring:function(s){var r=s.id;var q=c.springs[r];q.point1.connections--;q.point2.connections--;var p=$.inArray(q,k);if(p>-1){k.splice(p,1)}delete c.springs[r]},_update:function(p){d++;$.each(p,function(q,r){if(r.t in i){i[r.t](r)}});return d},tick:function(){i.tendParticles();i.eulerIntegrator(i.dt);i.tock()},tock:function(){var p=[];$.each(c.particles,function(r,q){p.push(r);p.push(q.p.x);p.push(q.p.y)});if(h){h({geometry:p,epoch:d,energy:b,bounds:g})}},tendParticles:function(){$.each(c.particles,function(q,p){if(p._m!==undefined){if(Math.abs(p.m-p._m)<1){p.m=p._m;delete p._m}else{p.m*=0.98}}p.v.x=p.v.y=0})},eulerIntegrator:function(p){if(i.repulsion>0){if(i.theta>0){i.applyBarnesHutRepulsion()}else{i.applyBruteForceRepulsion()}}if(i.stiffness>0){i.applySprings()}i.applyCenterDrift();if(i.gravity){i.applyCenterGravity()}i.updateVelocity(p);i.updatePosition(p)},applyBruteForceRepulsion:function(){$.each(c.particles,function(q,p){$.each(c.particles,function(s,r){if(p!==r){var u=p.p.subtract(r.p);var v=Math.max(1,u.magnitude());var t=((u.magnitude()>0)?u:Point.random(1)).normalize();p.applyForce(t.multiply(i.repulsion*(r._m||r.m)*0.5).divide(v*v*0.5));r.applyForce(t.multiply(i.repulsion*(p._m||p.m)*0.5).divide(v*v*-0.5))}})})},applyBarnesHutRepulsion:function(){if(!g.topleft||!g.bottomright){return}var q=new Point(g.bottomright);var p=new Point(g.topleft);f.init(p,q,i.theta);$.each(c.particles,function(s,r){f.insert(r)});$.each(c.particles,function(s,r){f.applyForces(r,i.repulsion)})},applySprings:function(){$.each(c.springs,function(t,p){var s=p.point2.p.subtract(p.point1.p);var q=p.length-s.magnitude();var r=((s.magnitude()>0)?s:Point.random(1)).normalize();p.point1.applyForce(r.multiply(p.k*q*-0.5));p.point2.applyForce(r.multiply(p.k*q*0.5))})},applyCenterDrift:function(){var q=0;var r=new Point(0,0);$.each(c.particles,function(t,s){r.add(s.p);q++});if(q==0){return}var p=r.divide(-q);$.each(c.particles,function(t,s){s.applyForce(p)})},applyCenterGravity:function(){$.each(c.particles,function(r,p){var q=p.p.multiply(-1);p.applyForce(q.multiply(i.repulsion/100))})},updateVelocity:function(p){$.each(c.particles,function(t,q){if(q.fixed){q.v=new Point(0,0);q.f=new Point(0,0);return}var s=q.v.magnitude();q.v=q.v.add(q.f.multiply(p)).multiply(1-i.friction);q.f.x=q.f.y=0;var r=q.v.magnitude();if(r>j){q.v=q.v.divide(r*r)}})},updatePosition:function(q){var r=0,p=0,u=0;var t=null;var s=null;$.each(c.particles,function(w,v){v.p=v.p.add(v.v.multiply(q));var x=v.v.magnitude();var z=x*x;r+=z;p=Math.max(z,p);u++;if(!t){t=new Point(v.p.x,v.p.y);s=new Point(v.p.x,v.p.y);return}var y=v.p;if(y.x===null||y.y===null){return}if(y.x>t.x){t.x=y.x}if(y.y>t.y){t.y=y.y}if(y.x<s.x){s.x=y.x}if(y.y<s.y){s.y=y.y}});b={sum:r,max:p,mean:r/u,n:u};g={topleft:s||new Point(-1,-1),bottomright:t||new Point(1,1)}},systemEnergy:function(p){return b}};return i.init()};var _nearParticle=function(b,c){var c=c||0;var a=b.x;var f=b.y;var e=c*2;return new Point(a-c+Math.random()*e,f-c+Math.random()*e)};
 
diff --git a/src/physics/system.js b/src/physics/system.js
index 2e7fa65..b1b722f 100644
--- a/src/physics/system.js
+++ b/src/physics/system.js
@@ -392,6 +392,9 @@
       
       // convert to/from screen coordinates
       screen:function(opts){
+        if (opts == undefined) return {size:(_screenSize)? objcopy(_screenSize) : undefined, 
+                                       padding:_screenPadding.concat(), 
+                                       step:_screenStep}
         if (opts.size!==undefined) that.screenSize(opts.size.width, opts.size.height)
         if (!isNaN(opts.step)) that.screenStep(opts.step)
         if (opts.padding!==undefined) that.screenPadding(opts.padding)