html, body, #container {

    width: 100%;

    height: 100%;

    margin: 0;

    padding: 0;

}

anychart.onDocumentReady(function() {

    // create chart

    chart = anychart.surface()

    // set data

    chart.data(generateData(hyperbolicParaboloid));

​

    // create color scale

    var colorScale = anychart.scales.ordinalColor();

​

    // set ranges

    colorScale.ranges([

        {less: -10, color: "#dd2c00"},

        {from: -10, to: 5, color: "#ffd54f"},

        {greater: 5,color: "#00bfa5" }

    ]);

​

    // set color scale

    chart.colorScale(colorScale);

​

    // display chart

    chart.container('container').draw();

});

// generate a data set from function

var generateData = function(z_function) {

  var max_val = 5;

  var step = 0.5;

  var output = [];

  for (var x = -max_val; x <= max_val; x += step) {

    for (var y = -max_val; y <= max_val; y += step) {

      output.push([x, y, z_function(x, y)]);

    }

  }

  return output;

};

// hyperbolic paraboloid function

var hyperbolicParaboloid = function(x, y) {

  return Math.pow(y,2)-Math.pow(x,2);

};