ermine to determine
		//the max value of Y axis. Only happens one time when loading the webpage.
		const kde = kernelDensityEstimation(data, min_slider);
		const v = new Array(n);
		for (let i=0; i<n;i++){ v[i] = kde(x[i]);}
		const maxYkde = d3.max(v),
		      maxYhist = d3.max(histogram(data, max_slider, min, max));

		//background
		pdfgraph
		    .append("rect")
  		    .attr("x", 0)
  		    .attr("y", 0)
  		    .attr("width", innerW)
  		    .attr("height", innerH)
  		    .attr("class","background ax