/* ASCIIsvg.js
  ==============
  JavaScript routines to dynamically generate Scalable Vector Graphics
  using a mathematical xy-coordinate system (y increases upwards) and
  very intuitive JavaScript commands (no programming experience required).
  ASCIIsvg.js is good for learning math and illustrating online math texts.
  Works with Internet Explorer+Adobe SVGviewer and SVG enabled Mozilla/Firefox.
  
  Ver 1.2.6 Aug 1, 2005 (c) Peter Jipsen http://www.chapman.edu/~jipsen
  Latest version at http://www.chapman.edu/~jipsen/svg/ASCIIsvg.js
  If you use it on a webpage, please send the URL to jipsen@chapman.edu
  
  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or (at
  your option) any later version.
  
  This program is distributed in the hope that it will be useful, 
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  General Public License (at http://www.gnu.org/copyleft/gpl.html) 
  for more details.*/
  
  var checkIfSVGavailable = true;
  var notifyIfNoSVG = true;
  var xunitlength = 20;  // pixels
  var yunitlength = 20;  // pixels
  var origin = [0,0];   // in pixels (default is bottom left corner)
  var border = 25;
  var strokewidth = "1"; // pixel
  var strokedasharray;   // e.g. 4,4 pixel
  var stroke = "black"; // default line color
  var fill = "none";    // default fill color
  var fontstyle = "italic"; // default shape for text labels
  var fontfamily = "times"; // default font
  var fontsize = "20";      // default size
  var fontweight = "normal";// default size
  var fontstroke = "none";  // default font outline color
  var fontfill = "none";    // default font color
  var markerstrokewidth = "1";
  var markerstroke = "black";
  var markerfill = "yellow";
  var marker = "none";
  var arrowfill = stroke;
  var dotradius = 4;
  var ticklength = 4;
  var axesstroke = "black";
  var gridstroke = "grey";
  var pointerpos = null;
  var coordinates = null;
  var above = "above";
  var below = "below";
  var left = "left";
  var right = "right";
  var aboveleft = "aboveleft";
  var aboveright = "aboveright";
  var belowleft = "belowleft";
  var belowright = "belowright";
  var cpi = "\u03C0", ctheta = "\u03B8";
  var pi = Math.PI, ln = Math.log, e = Math.E;
  var arcsin = Math.asin, arccos = Math.acos, arctan = Math.atan;
  var sec = function(x) { return 1/Math.cos(x) };
  var csc = function(x) { return 1/Math.sin(x) };
  var cot = function(x) { return 1/Math.tan(x) };
  var xMin=-5;
  var xMax=5;
  var yMin=-5;
  var yMax=5;
  var isIE = document.createElementNS==null;
  var picture, svgpicture, doc, width, height, a, b, c, d, i, n, p, t, x, y;
  var arcsec = function(x) { return arccos(1/x) };
  var arccsc = function(x) { return arcsin(1/x) };
  var arccot = function(x) { return arctan(1/x) };
  var sinh = function(x) { return (Math.exp(x)-Math.exp(-x))/2 };
  var cosh = function(x) { return (Math.exp(x)+Math.exp(-x))/2 };
  var tanh = 
    function(x) { return (Math.exp(x)-Math.exp(-x))/(Math.exp(x)+Math.exp(-x)) };
  var sech = function(x) { return 1/cosh(x) };
  var csch = function(x) { return 1/sinh(x) };
  var coth = function(x) { return 1/tanh(x) };
  var arcsinh = function(x) { return ln(x+Math.sqrt(x*x+1)) };
  var arccosh = function(x) { return ln(x+Math.sqrt(x*x-1)) };
  var arctanh = function(x) { return ln((1+x)/(1-x))/2 };
  var sech = function(x) { return 1/cosh(x) };
  var csch = function(x) { return 1/sinh(x) };
  var coth = function(x) { return 1/tanh(x) };
  var arcsech = function(x) { return arccosh(1/x) };
  var arccsch = function(x) { return arcsinh(1/x) };
  var arccoth = function(x) { return arctanh(1/x) };
  var sign = function(x) { return (x==0?0:(x<0?-1:1)) };
  
  function factorial(x,n) {
    if (n==null) n=1;
    for (var i=x-n; i>0; i-=n) x*=i;
    return (x<0?NaN:(x==0?1:x));
  }
  
  function C(x,k) {
    var res=1;
    for (var i=0; i<k; i++) res*=(x-i)/(k-i);
    return res;
  }
  
  function chop(x,n) {
    if (n==null) n=0;
    return Math.floor(x*Math.pow(10,n))/Math.pow(10,n);
  }
  
  function ran(a,b,n) {
    if (n==null) n=0;
    return chop((b+Math.pow(10,-n)-a)*Math.random()+a,n);
  }
  
  function myCreateElementXHTML(t) {
    if (isIE) return document.createElement(t);
    else return document.createElementNS("http://www.w3.org/1999/xhtml",t);
  }
  
  function isSVGavailable() {
    var nd = myCreateElementXHTML("center");
    nd.appendChild(document.createTextNode("To view the "));
    var an = myCreateElementXHTML("a");
    an.appendChild(document.createTextNode("ASCIIsvg"));
    an.setAttribute("href","http://www.chapman.edu/~jipsen/asciisvg.html");
    nd.appendChild(an);
    nd.appendChild(document.createTextNode(" images use Internet Explorer 6+"));
    an = myCreateElementXHTML("a");
    an.appendChild(document.createTextNode("Adobe SVGviewer 3.02"));
    an.setAttribute("href","http://www.adobe.com/svg");
    nd.appendChild(an);
    nd.appendChild(document.createTextNode(" or "));
    an = myCreateElementXHTML("a");
    an.appendChild(document.createTextNode("SVG enabled Mozilla/Firefox"));
    an.setAttribute("href",
      "http://www.chapman.edu/~jipsen/svg/svgenabledmozillafirefox.html");
    nd.appendChild(an);
    if (navigator.appName.slice(0,8)=="Netscape") 
      if (window['SVGElement']) return null;
      else return nd;
    else if (navigator.appName.slice(0,9)=="Microsoft")
      try        {
        var oSVG=eval("new ActiveXObject('Adobe.SVGCtl.3');");
          return null;
      } catch (e) {
          return nd;
      }
    else return nd;
  }
  
  function less(x,y) { return x < y }  // used for scripts in XML files
                                       // since IE does not handle CDATA well
  function setText(st,id) { 
    var node = document.getElementById(id);
    if (node!=null)
      if (node.childNodes.length!=0) node.childNodes[0].nodeValue = st;
      else node.appendChild(document.createTextNode(st));
  }
  
  function myCreateElementSVG(t) {
    if (isIE) return doc.createElement(t);
    else return doc.createElementNS("http://www.w3.org/2000/svg",t);
  }
  
  function getX() {
    return (doc.getElementById("pointerpos").getAttribute("cx")-origin[0])/xunitlength;
  }
  
  function getY() {
    return (height-origin[1]-doc.getElementById("pointerpos").getAttribute("cy"))/yunitlength;
  }
  
  function mousemove_listener(evt) {
    if (svgpicture.getAttribute("xbase")!=null)
      pointerpos.cx.baseVal.value = evt.clientX-svgpicture.getAttribute("xbase");
    if (svgpicture.getAttribute("ybase")!=null)
      pointerpos.cy.baseVal.value = evt.clientY-svgpicture.getAttribute("ybase");
  }
  
  function top_listener(evt) {
    svgpicture.setAttribute("ybase",evt.clientY);
  }
  
  function bottom_listener(evt) { 
    svgpicture.setAttribute("ybase",evt.clientY-height+1);
  }
  
  function left_listener(evt) {
    svgpicture.setAttribute("xbase",evt.clientX);
  }
  
  function right_listener(evt) {
    svgpicture.setAttribute("xbase",evt.clientX-width+1);
  }
  
  function switchTo(id) {
    picture = document.getElementById(id);
    width = picture.getAttribute("width")-0;
    height = picture.getAttribute("height")-0;
    strokewidth = "1" // pixel
    stroke = "black"; // default line color
    fill = "none";    // default fill color
    marker = "none";
    if ((picture.nodeName == "EMBED" || picture.nodeName == "embed") && isIE) {
      svgpicture = picture.getSVGDocument().getElementById("root");
      doc = picture.getSVGDocument();
    } else {
      svgpicture = picture;
      doc = document;
    }
    xunitlength = svgpicture.getAttribute("xunitlength")-0;
    yunitlength = svgpicture.getAttribute("yunitlength")-0;
    origin = [svgpicture.getAttribute("ox")-0,svgpicture.getAttribute("oy")-0];
  }
  
  function drawPictures() {
   var src, id, dsvg, onmov, nd;
    var pictures = document.getElementsByTagName("embed");
    var len = pictures.length;
   if (checkIfSVGavailable) {
    nd = isSVGavailable();
    if (nd != null && notifyIfNoSVG && len>0) {
      var ASbody = document.getElementsByTagName("body")[0];
      ASbody.insertBefore(nd,ASbody.childNodes[0]);
    }
   }
   if (nd == null) {
    for (var index = 0; index < len; index++) {
      picture = (isIE ? pictures[index] : pictures[0]);
      src = picture.getAttribute("script");
      if (src==null) src = "";
      if (src=="") {
        if (document.getElementById("picture"+(index+1)+"input")==null) {
          node = picture.previousSibling;
          while (node != null && node.nodeName != "TEXTAREA" && 
            node.nodeName != "textarea") node = node.previousSibling;
          if (node.value.indexOf("hideCode()")!=-1) {
            node.style.display = "none";
            node.nextSibling.nextSibling.style.display = "none";
          }
          node.setAttribute("id","picture"+(index+1)+"input");
        }
        src = document.getElementById("picture"+(index+1)+"input").value;
      }
      src = src.replace(/plot\(\x20*([^\"\[].*?) /g,"plot\(\"$1\",");
      src = src.replace(/plot\(\x20*([^\"\[].*)\)/g,"plot(\"$1\")");
      src = src.replace(/([0-9])([a-zA-Z])/g,"$1*$2");
      src = src.replace(/\)([\(0-9a-zA-Z])/g,"\)*$1");
  //    eval(src.replace(/\s\s/g,";")); //for XML version
      id = picture.getAttribute("id");
      dsvg = picture.getAttribute("src");
      onmov = picture.getAttribute("onmousemove");
      if (id == null || id == "") {
        id = "picture"+(index+1);
        picture.setAttribute("id",id);
      }
      try {
        with (Math) eval(src);
      } catch(err) {alert(err+"\n"+src)}
      if (isIE) src = src.replace(/([^\r])\n/g,"$1\r");
      setText("<embed width=\""+width+"\" height=\""+height+"\" src=\""+
              dsvg+"\" "+(onmov!=null?"onmousemove=\""+onmov+"\"":"")+
              (isIE?"\r":"\n")+"script=\'"+src+"\'>",id+"script");
  //    setText(src.replace(/\s\s/g,"\r"),id+"script"); //for XML version
    }
   }
  }
  
  function updatePicture(obj) {
    var src = document.getElementById("picture"+(obj+1)+"input").value;
  //  picture = document.getElementById("picture"+(obj+1));//id);
    switchTo("picture"+(obj+1));
    src = src.replace(/plot\(\x20*([^\"\[].*?) /g,"plot\(\"$1\",");
    src = src.replace(/plot\(\x20*([^\"\[].*)\)/g,"plot(\"$1\")");
    src = src.replace(/([0-9])([a-zA-Z])/g,"$1*$2");
    src = src.replace(/\)([\(0-9a-zA-Z])/g,"\)*$1");
    with (Math) eval(src);
  }
  
  function showHideCode(obj) {
    var node = obj.previousSibling;
    while (node != null && node.nodeName != "BUTTON" && 
      node.nodeName != "button") node = node.previousSibling;
    if (node.style.display == "none") node.style.display = "";
    else node.style.display = "none";
    while (node != null && node.nodeName != "TEXTAREA" && 
      node.nodeName != "textarea") node = node.previousSibling;
    if (node.style.display == "none") node.style.display = "";
    else node.style.display = "none";
  }
  
  function hideCode() { //do nothing
  }
  
  function setBorder(x) { border = x }
  
  function initPicture(xmin,xmax,ymin,ymax) {
    strokewidth = "1"; // pixel
    strokedasharray = null;
    stroke = "black"; // default line color
    fill = "none";    // default fill color
    fontstyle = "italic"; // default shape for text labels
    fontfamily = "times"; // default font
    fontsize = "20";      // default size
    fontweight = "normal";
    marker = "none";
    xMin = xmin;
    xMax = xmax;
   if (typeof xmin != "number" || typeof xmax != "number" || xmin >= xmax) 
     alert("initPicture requires at least two numbers: xmin < xmax");
   else if (ymax != null && (typeof ymin != "number" || 
            typeof ymax != "number" || ymin >= ymax))
     alert("initPicture(xmin,xmax,ymin,ymax) requires numbers ymin < ymax");
   else {
    if (ymin!=null) yMin = ymin;
    if (ymax!=null) yMax = ymax;
    if (width==null) width = picture.getAttribute("width");
    else picture.setAttribute("width",width);
    if (height==null) height = picture.getAttribute("height");
    else picture.setAttribute("height",height);
    if (xmax!=null) {
      xunitlength = (width-2*border)/(xmax-xmin);
      yunitlength = xunitlength;
      if (ymin==null) {
        origin = [-xmin*xunitlength+border,height/2];
        yMin = -(height-2*border)/(2*yunitlength);
        yMax = -yMin;
      } else {
        if (ymax!=null) yunitlength = (height-2*border)/(ymax-ymin);
        else yMax = (height-2*border)/yunitlength + ymin;
        origin = [-xmin*xunitlength+border,-ymin*yunitlength+border];
      }
    }
    if (picture.nodeName == "EMBED" || picture.nodeName == "embed") {
      if (isIE) {
        svgpicture = picture.getSVGDocument().getElementById("root");
        while (svgpicture.childNodes.length()>5) 
          svgpicture.removeChild(svgpicture.lastChild); 
        svgpicture.setAttribute("width",width);
        svgpicture.setAttribute("height",height);
        doc = picture.getSVGDocument();
      } else {
        var qnode = document.createElementNS("http://www.w3.org/2000/svg","svg");
        qnode.setAttribute("id",picture.getAttribute("id"));
        qnode.setAttribute("width",picture.getAttribute("width"));
        qnode.setAttribute("height",picture.getAttribute("height"));
        if (picture.parentNode!=null)
          picture.parentNode.replaceChild(qnode,picture);
        else
          svgpicture.parentNode.replaceChild(qnode,svgpicture);
        svgpicture = qnode;
        doc = document;
        pointerpos = doc.getElementById("pointerpos");
        if (pointerpos==null) {
          pointerpos = myCreateElementSVG("circle");
          pointerpos.setAttribute("id","pointerpos");
          pointerpos.setAttribute("cx",0);
          pointerpos.setAttribute("cy",0);
          pointerpos.setAttribute("r",0.5);
          pointerpos.setAttribute("fill","red");
          svgpicture.appendChild(pointerpos);
        }
        alert('Click OK');
      }
    } else {
      svgpicture = picture;
      doc = document;
    }
    svgpicture.setAttribute("xunitlength",xunitlength);
    svgpicture.setAttribute("yunitlength",yunitlength);
    svgpicture.setAttribute("ox",origin[0]);
    svgpicture.setAttribute("oy",origin[1]);
    var node = myCreateElementSVG("rect");
    node.setAttribute("x","0");
    node.setAttribute("y","0");
    node.setAttribute("width",width);
    node.setAttribute("height",height);
    node.setAttribute("style","stroke-width:1;fill:white");
    svgpicture.appendChild(node);
    if (!isIE && picture.getAttribute("onmousemove")!=null) {
      svgpicture.addEventListener("mousemove", mousemove_listener, true);
      var st = picture.getAttribute("onmousemove");
      svgpicture.addEventListener("mousemove", eval(st.slice(0,st.indexOf("("))), true);
      node = myCreateElementSVG("polyline");
      node.setAttribute("points","0,0 "+width+",0");
      node.setAttribute("style","stroke:white; stroke-width:3");
      node.addEventListener("mousemove", top_listener, true);
      svgpicture.appendChild(node);
      node = myCreateElementSVG("polyline");
      node.setAttribute("points","0,"+height+" "+width+","+height);
      node.setAttribute("style","stroke:white; stroke-width:3");
      node.addEventListener("mousemove", bottom_listener, true);
      svgpicture.appendChild(node);
      node = myCreateElementSVG("polyline");
      node.setAttribute("points","0,0 0,"+height);
      node.setAttribute("style","stroke:white; stroke-width:3");
      node.addEventListener("mousemove", left_listener, true);
      svgpicture.appendChild(node);
      node = myCreateElementSVG("polyline");
      node.setAttribute("points",(width-1)+",0 "+(width-1)+","+height);
      node.setAttribute("style","stroke:white; stroke-width:3");
      node.addEventListener("mousemove", right_listener, true);
      svgpicture.appendChild(node);
    }
    border = 25;
   }
  }
  
  function line(p,q,id) { // segment connecting points p,q (coordinates in units)
    var node;
    if (id!=null) node = doc.getElementById(id);
    if (node==null) {
      node = myCreateElementSVG("path");
      node.setAttribute("id", id);
      svgpicture.appendChild(node);
    }
    node.setAttribute("d","M"+(p[0]*xunitlength+origin[0])+","+
      (height-p[1]*yunitlength-origin[1])+" "+
      (q[0]*xunitlength+origin[0])+","+(height-q[1]*yunitlength-origin[1]));
    node.setAttribute("stroke-width", strokewidth);
    if (strokedasharray!=null) 
      node.setAttribute("stroke-dasharray", strokedasharray);
    node.setAttribute("stroke", stroke);
    node.setAttribute("fill", fill);
    if (marker=="dot" || marker=="arrowdot") {
      ASdot(p,4,markerstroke,markerfill);
      if (marker=="arrowdot") arrowhead(p,q);
      ASdot(q,4,markerstroke,markerfill);
    } else if (marker=="arrow") arrowhead(p,q);
  }
  
  function path(plist,id,c) {
    if (c==null) c="";
    var node, st, i;
    if (id!=null) node = doc.getElementById(id);
    if (node==null) {
      node = myCreateElementSVG("path");
      node.setAttribute("id", id);
      svgpicture.appendChild(node);
    }
    if (typeof plist == "string") st = plist;
    else {
      st = "M";
      st += (plist[0][0]*xunitlength+origin[0])+","+
            (height-plist[0][1]*yunitlength-origin[1])+" "+c;
      for (i=1; i<plist.length; i++)
        st += (plist[i][0]*xunitlength+origin[0])+","+
              (height-plist[i][1]*yunitlength-origin[1])+" ";
    }
    node.setAttribute("d", st);
    node.setAttribute("stroke-width", strokewidth);
    if (strokedasharray!=null) 
      node.setAttribute("stroke-dasharray", strokedasharray);
    node.setAttribute("stroke", stroke);
    node.setAttribute("fill", fill);
    if (marker=="dot" || marker=="arrowdot")
      for (i=0; i<plist.length; i++)
        if (c!="C" || i!=1 && i!=2)
          ASdot(plist[i],4,markerstroke,markerfill);
  }
  
  function curve(plist,id) {
    path(plist,id,"T");
  }
  
  function circle(center,radius,id) { // coordinates in units
    var node;
    if (id!=null) node = doc.getElementById(id);
    if (node==null) {
      node = myCreateElementSVG("circle");
      node.setAttribute("id", id);
      svgpicture.appendChild(node);
    }
    node.setAttribute("cx",center[0]*xunitlength+origin[0]);
    node.setAttribute("cy",height-center[1]*yunitlength-origin[1]);
    node.setAttribute("r",radius*xunitlength);
    node.setAttribute("stroke-width", strokewidth);
    node.setAttribute("stroke", stroke);
    node.setAttribute("fill", fill);
  }
  
  function arc(start,end,radius,id) { // coordinates in units
    var node;
    if (id!=null) node = doc.getElementById(id);
    if (node==null) {
      node = myCreateElementSVG("path");
      node.setAttribute("id", id);
      svgpicture.appendChild(node);
    }
    node.setAttribute("d","M"+(start[0]*xunitlength+origin[0])+","+
      (height-start[1]*yunitlength-origin[1])+" A"+radius*xunitlength+","+
       radius*xunitlength+" 0 0,0 "+(end[0]*xunitlength+origin[0])+","+
      (height-end[1]*yunitlength-origin[1]));
    node.setAttribute("stroke-width", strokewidth);
    node.setAttribute("stroke", stroke);
    node.setAttribute("fill", fill);
  }
  
  function ellipse(center,rx,ry,id) { // coordinates in units
    var node;
    if (id!=null) node = doc.getElementById(id);
    if (node==null) {
      node = myCreateElementSVG("ellipse");
      node.setAttribute("id", id);
      svgpicture.appendChild(node);
    }
    node.setAttribute("cx",center[0]*xunitlength+origin[0]);
    node.setAttribute("cy",height-center[1]*yunitlength-origin[1]);
    node.setAttribute("rx",rx*xunitlength);
    node.setAttribute("ry",ry*yunitlength);
    node.setAttribute("stroke-width", strokewidth);
    node.setAttribute("stroke", stroke);
    node.setAttribute("fill", fill);
  }
  
  function rect(p,q,id,rx,ry) { // opposite corners in units, rounded by radii
    var node;
    if (id!=null) node = doc.getElementById(id);
    if (node==null) {
      node = myCreateElementSVG("rect");
      node.setAttribute("id", id);
      svgpicture.appendChild(node);
    }
    node.setAttribute("x",p[0]*xunitlength+origin[0]);
    node.setAttribute("y",height-q[1]*yunitlength-origin[1]);
    node.setAttribute("width",(q[0]-p[0])*xunitlength);
    node.setAttribute("height",(q[1]-p[1])*yunitlength);
    if (rx!=null) node.setAttribute("rx",rx*xunitlength);
    if (ry!=null) node.setAttribute("ry",ry*yunitlength);
    node.setAttribute("stroke-width", strokewidth);
    node.setAttribute("stroke", stroke);
    node.setAttribute("fill", fill);
  }
  
  function text(p,st,pos,id) {
    var textanchor = "middle";
    var dx = 0; var dy = 5;
    if (pos!=null) {
      if (pos.slice(0,5)=="above") dy = -10;
      if (pos.slice(0,5)=="below") dy = 20;
      if (pos.slice(0,5)=="right" || pos.slice(5,10)=="right") {
        textanchor = "start";
        dx = 8;
      }
      if (pos.slice(0,4)=="left" || pos.slice(5,9)=="left") {
        textanchor = "end";
        dx = -8;
      }
    }
    var node;
    if (id!=null) node = doc.getElementById(id);
    if (node==null) {
      node = myCreateElementSVG("text");
      node.setAttribute("id", id);
      svgpicture.appendChild(node);
      node.appendChild(doc.createTextNode(st));
    }
    node.lastChild.nodeValue = st;
    node.setAttribute("x",p[0]*xunitlength+origin[0]+dx);
    node.setAttribute("y",height-p[1]*yunitlength-origin[1]+dy);
    node.setAttribute("font-style",fontstyle);
    node.setAttribute("font-family",fontfamily);
    node.setAttribute("font-size",fontsize);
    node.setAttribute("font-weight",fontweight);
    node.setAttribute("text-anchor",textanchor);
    if (fontstroke!="none") node.setAttribute("stroke",fontstroke);
    if (fontfill!="none") node.setAttribute("fill",fontfill);
    return p;
  }
  
  function ASdot(center,radius,s,f) { // coordinates in units, radius in pixel
    if (s==null) s = stroke; if (f==null) f = fill;
    var node = myCreateElementSVG("circle");
    node.setAttribute("cx",center[0]*xunitlength+origin[0]);
    node.setAttribute("cy",height-center[1]*yunitlength-origin[1]);
    node.setAttribute("r",radius);
    node.setAttribute("stroke-width", strokewidth);
    node.setAttribute("stroke", s);
    node.setAttribute("fill", f);
    svgpicture.appendChild(node);
  }
  
  function dot(center, typ, label, pos, id) {
    var node;
    var cx = center[0]*xunitlength+origin[0];
    var cy = height-center[1]*yunitlength-origin[1];
    if (id!=null) node = doc.getElementById(id);
    if (typ=="+" || typ=="-" || typ=="|") {
      if (node==null) {
        node = myCreateElementSVG("path");
        node.setAttribute("id", id);
        svgpicture.appendChild(node);
      }
      if (typ=="+") {
        node.setAttribute("d",
          " M "+(cx-ticklength)+" "+cy+" L "+(cx+ticklength)+" "+cy+
          " M "+cx+" "+(cy-ticklength)+" L "+cx+" "+(cy+ticklength));
        node.setAttribute("stroke-width", .5);
        node.setAttribute("stroke", axesstroke);
      } else {
        if (typ=="-") node.setAttribute("d",
          " M "+(cx-ticklength)+" "+cy+" L "+(cx+ticklength)+" "+cy);
        else node.setAttribute("d",
          " M "+cx+" "+(cy-ticklength)+" L "+cx+" "+(cy+ticklength));
        node.setAttribute("stroke-width", strokewidth);
        node.setAttribute("stroke", stroke);
      }
    } else {
      if (node==null) {
        node = myCreateElementSVG("circle");
        node.setAttribute("id", id);
        svgpicture.appendChild(node);
      }
      node.setAttribute("cx",cx);
      node.setAttribute("cy",cy);
      node.setAttribute("r",dotradius);
      node.setAttribute("stroke-width", strokewidth);
      node.setAttribute("stroke", stroke);
      node.setAttribute("fill", (typ=="open"?"white":stroke));
    }
    if (label!=null) 
      text(center,label,(pos==null?"below":pos),(id==null?id:id+"label"))
  }
  
  function arrowhead(p,q) { // draw arrowhead at q (in units)
    var up;
    var v = [p[0]*xunitlength+origin[0],height-p[1]*yunitlength-origin[1]];
    var w = [q[0]*xunitlength+origin[0],height-q[1]*yunitlength-origin[1]];
    var u = [w[0]-v[0],w[1]-v[1]];
    var d = Math.sqrt(u[0]*u[0]+u[1]*u[1]);
    if (d > 0.00000001) {
      u = [u[0]/d, u[1]/d];
      up = [-u[1],u[0]];
      var node = myCreateElementSVG("path");
      node.setAttribute("d","M "+(w[0]-15*u[0]-4*up[0])+" "+
        (w[1]-15*u[1]-4*up[1])+" L "+(w[0]-3*u[0])+" "+(w[1]-3*u[1])+" L "+
        (w[0]-15*u[0]+4*up[0])+" "+(w[1]-15*u[1]+4*up[1])+" z");
      node.setAttribute("stroke-width", markerstrokewidth);
      node.setAttribute("stroke", stroke); /*was markerstroke*/
      node.setAttribute("fill", stroke); /*was arrowfill*/
      svgpicture.appendChild(node);    
    }
  }
  
  function chopZ(st) {
    var k = st.indexOf(".");
    if (k==-1) return st;
    for (var i=st.length-1; i>k && st.charAt(i)=="0"; i--);
    if (i==k) i--;
    return st.slice(0,i+1);
  }
  
  function grid(dx,dy) { // for backward compatibility
    axes(dx,dy,null,dx,dy)
  }
  
  function axes(dx,dy,labels,gdx,gdy) {
    var x, y, ldx, ldy, pnode, st;
    if (typeof dx=="string") { labels = dx; dx = null; }
    if (typeof dy=="string") { gdx = dy; dy = null; }
    dx = (dx==null?xunitlength:dx*xunitlength);
    dy = (dy==null?yunitlength:dy*yunitlength);
    if (gdx!=null) {
      gdx = (typeof gdx=="string"?dx:gdx*xunitlength);
      gdy = (gdy==null?dy:gdy*yunitlength);
      pnode = myCreateElementSVG("path");
      st="";
      for (x = origin[0]; x<width; x = x+gdx)
        st += " M"+x+",0"+" "+x+","+height;
      for (x = origin[0]-gdx; x>0; x = x-gdx)
        st += " M"+x+",0"+" "+x+","+height;
      for (y = height-origin[1]; y<height; y = y+gdy)
        st += " M0,"+y+" "+width+","+y;
      for (y = height-origin[1]-gdy; y>0; y = y-gdy)
        st += " M0,"+y+" "+width+","+y;
      pnode.setAttribute("d",st);
      pnode.setAttribute("stroke-width", .5);
      pnode.setAttribute("stroke", gridstroke);
      pnode.setAttribute("fill", fill);
      svgpicture.appendChild(pnode);
    }
    pnode = myCreateElementSVG("path");
    st="M0,"+(height-origin[1])+" "+width+","+
      (height-origin[1])+" M"+origin[0]+",0 "+origin[0]+","+height;
    for (x = origin[0]+dx; x<width; x = x+dx)
      st += " M"+x+","+(height-origin[1]+ticklength)+" "+x+","+
             (height-origin[1]-ticklength);
    for (x = origin[0]-dx; x>0; x = x-dx)
      st += " M"+x+","+(height-origin[1]+ticklength)+" "+x+","+
             (height-origin[1]-ticklength);
    for (y = height-origin[1]+dy; y<height; y = y+dy)
      st += " M"+(origin[0]+ticklength)+","+y+" "+(origin[0]-ticklength)+","+y;
    for (y = height-origin[1]-dy; y>0; y = y-dy)
      st += " M"+(origin[0]+ticklength)+","+y+" "+(origin[0]-ticklength)+","+y;
    if (labels!=null) with (Math) {
      ldx = dx/xunitlength;
      ldy = dy/yunitlength;
      var ddx = floor(1.1-log(ldx)/log(10));
      var ddy = floor(1.1-log(ldy)/log(10));
      for (x = ldx; x<=xMax; x = x+ldx)
        text([x,0],chopZ(x.toFixed(ddx)),"below");
      for (x = -ldx; xMin<=x; x = x-ldx)
        text([x,0],chopZ(x.toFixed(ddx)),"below");
      for (y = ldy; y<=yMax; y = y+ldy)
        text([0,y],chopZ(y.toFixed(ddy)),"left");
      for (y = -ldy; yMin<=y; y = y-ldy)
        text([0,y],chopZ(y.toFixed(ddy)),"left");
    }
    pnode.setAttribute("d",st);
    pnode.setAttribute("stroke-width", .5);
    pnode.setAttribute("stroke", axesstroke);
    pnode.setAttribute("fill", fill);
    svgpicture.appendChild(pnode);
  }
  
  function mathjs(st) {
    //translate a math formula to js function notation
    // a^b --> pow(a,b)
    // na --> n*a
    // (...)d --> (...)*d
    // n! --> factorial(n)
    // sin^-1 --> arcsin etc.
    //while ^ in string, find term on left and right
    //slice and concat new formula string
    st = st.replace(/\s/g,"");
    if (st.indexOf("^-1")!=-1) {
      st = st.replace(/sin^-1/g,"arcsin");
      st = st.replace(/cos^-1/g,"arccos");
      st = st.replace(/tan^-1/g,"arctan");
      st = st.replace(/sec^-1/g,"arcsec");
      st = st.replace(/csc^-1/g,"arccsc");
      st = st.replace(/cot^-1/g,"arccot");
      st = st.replace(/sinh^-1/g,"arcsinh");
      st = st.replace(/cosh^-1/g,"arccosh");
      st = st.replace(/tanh^-1/g,"arctanh");
      st = st.replace(/sech^-1/g,"arcsech");
      st = st.replace(/csch^-1/g,"arccsch");
      st = st.replace(/coth^-1/g,"arccoth");
    }
    st = st.replace(/^e<st.length && (ch=st.charAt(k))>="0" && ch<="9") k++;
        if (ch==".") {
          k++;
          while (k<st.length && (ch=st.charAt(k))>="0" && ch<="9") k++;
        }
      } else if (ch=="(") {// look for matching closing bracket and function name
        nested = 1;
        k++;
        while (k<st.length && nested>0) {
          ch = st.charAt(k);
          if (ch=="(") nested++;
          else if (ch==")") nested--;
          k++;
        }
      } else if (ch>="a" && ch<="z" || ch>="A" && ch<="Z") {// look for variable
        k++;
        while (k<st.length && (ch=st.charAt(k))>="a" && ch<="z" ||
                 ch>="A" && ch<="Z") k++;
      } else { 
        return "Error: incorrect syntax in "+st+" at position "+k;
      }
      st = st.slice(0,j+1)+"pow("+st.slice(j+1,i)+","+st.slice(i+1,k)+")"+
             st.slice(k);
    }
    while ((i=st.indexOf("!"))!=-1) {
      //find left argument
      if (i==0) return "Error: missing argument";
      j = i-1;
      ch = st.charAt(j);
      if (ch>="0" && ch<="9") {// look for (decimal) number
        j--;
        while (j>=0 && (ch=st.charAt(j))>="0" && ch<="9") j--;
        if (ch==".") {
          j--;
          while (j>=0 && (ch=st.charAt(j))>="0" && ch<="9") j--;
        }
      } else if (ch==")") {// look for matching opening bracket and function name
        nested = 1;
        j--;
        while (j>=0 && nested>0) {
          ch = st.charAt(j);
          if (ch=="(") nested--;
          else if (ch==")") nested++;
          j--;
        }
        while (j>=0 && (ch=st.charAt(j))>="a" && ch<="z" || ch>="A" && ch<="Z")
          j--;
      } else if (ch>="a" && ch<="z" || ch>="A" && ch<="Z") {// look for variable
        j--;
        while (j>=0 && (ch=st.charAt(j))>="a" && ch<="z" || ch>="A" && ch<="Z")
          j--;
      } else { 
        return "Error: incorrect syntax in "+st+" at position "+j;
      }
      st = st.slice(0,j+1)+"factorial("+st.slice(j+1,i)+")"+st.slice(i+1);
    }
    return st;
  }
  
  function plot(fun,xmin,xmax,points,id) {
    var pth = [];
    var f = function(x) { return x }, g = fun;
    var name = null;
    if (typeof fun=="string") 
      eval("g = function(x){ with(Math) return "+mathjs(fun)+" }");
    else if (typeof fun=="object") {
      eval("f = function(t){ with(Math) return "+mathjs(fun[0])+" }");
      eval("g = function(t){ with(Math) return "+mathjs(fun[1])+" }");
    }
    if (typeof xmin=="string") { name = xmin; xmin = xMin }
    else name = id;
    var min = (xmin==null?xMin:xmin);
    var max = (xmax==null?xMax:xmax);
    var inc = max-min-0.000001*(max-min);
    inc = (points==null?inc/200:inc/points);
    var gt;
  //alert(typeof g(min))
    for (var t = min; t <= max; t += inc) {
      gt = g(t);
      if (!(isNaN(gt)||Math.abs(gt)=="Infinity")) pth[pth.length] = [f(t), gt];
    }
    path(pth,name)
    return p;
  }
  
  function slopefield(fun,dx,dy) {
    var g = fun;
    if (typeof fun=="string") 
      eval("g = function(x,y){ with(Math) return "+mathjs(fun)+" }");
    var gxy,x,y,u,v,dz;
    if (dx==null) dx=1;
    if (dy==null) dy=1;
    dz = Math.sqrt(dx*dx+dy*dy)/6;
    var xmin = Math.ceil(xMin/dx);
    var ymin = Math.ceil(yMin/dy);
    for (x = xmin; x <= xMax; x += dx)
      for (y = ymin; y <= yMax; y += dy) {
        gxy = g(x,y);
        if (!isNaN(gxy)) {
          if (Math.abs(gxy)=="Infinity") {u = 0; v = dz;}
          else {u = dz/Math.sqrt(1+gxy*gxy); v = gxy*u;}
          line([x-u,y-v],[x+u,y+v]);
        }
      }
  }
  
  function updateCoords(ind) {
    switchTo("picture"+(ind+1));
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord"+ind);
  }
  
  function updateCoords0() {switchTo("picture1");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord0");}
  function updateCoords1() {switchTo("picture2");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord1");}
  function updateCoords2() {switchTo("picture3");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord2");}
  function updateCoords3() {switchTo("picture4");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord3");}
  function updateCoords4() {switchTo("picture5");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord4");}
  function updateCoords5() {switchTo("picture6");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord5");}
  function updateCoords6() {switchTo("picture7");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord6");}
  function updateCoords7() {switchTo("picture8");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord7");}
  function updateCoords8() {switchTo("picture9");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord8");}
  function updateCoords9() {switchTo("picture10");
    setText("("+getX().toFixed(2)+","+getY().toFixed(2)+")","AScoord9");}
  
  // GO1.1 Generic onload by Brothercake 
  // http://www.brothercake.com/
  //onload function
  function generic()
  {
    drawPictures();
  };
  //setup onload function
  if(typeof window.addEventListener != 'undefined')
  {
    //.. gecko, safari, konqueror and standard
    window.addEventListener('load', generic, false);
  }
  else if(typeof document.addEventListener != 'undefined')
  {
    //.. opera 7
    document.addEventListener('load', generic, false);
  }
  else if(typeof window.attachEvent != 'undefined')
  {
    //.. win/ie
    window.attachEvent('onload', generic);
  }
  //** remove this condition to degrade older browsers
  else
  {
    //.. mac/ie5 and anything else that gets this far
    //if there's an existing onload function
    if(typeof window.onload == 'function')
    {
      //store it
      var existing = onload;
      //add new onload handler
      window.onload = function()
      {
        //call existing onload function
        existing();
        //call generic onload function
        generic();
      };
    }
    else
    {
      //setup onload function
      window.onload = generic;
    }
  }