anychart.onDocumentReady(function() {
chart = anychart.surface()
chart.data(generateData(plane));
chart.stroke({color: '#ef6c00', thickness: 1, dash: '3 3'});
chart.container('container').draw();
var generateData = function(z_function) {
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)]);
var plane = function(x, y) {