function setExprFromHash(){

    var hash = getHashValue();
    if(hash){
      setExpr(hash);
    } else {
      setExpr(defaultExpr);
      setHashValue(expr);
    }

    // Update the text input to contain the updated expression.
    $('#inputField').val(expr);
  }
HTML5 Canvas Graphing Calculator
By Curran Kelleher 11/14/2013

Draws from examples found in
https://github.com/curran/screencasts/tree/gh-pages/grapher