function range(start, end){ //function that produces evenly spaced array
	var ra = [];
	var i_final = Math.round(end / 0.5);
	ra[0] = 0.0;
	for(var i=1; i<i_final; i++){
	ra[i] = ra[i-1] + 0.5;
	}
	console.log(ra)
	return ra;
}

//---- CHANGE Mach_sub and Mach_sup! -------
var Mach_sub = 0.5; //defines subsonic Mach number
var Mach_sup = 3.0; //defines supersonic Mach number
//-------------------------------------------


var width = 1000;
var height = 1000;
var xpos = 600, ypos = 200;
var textwidth = 150, textheight = 50;
						
var bubble_time = 4000; //duration of each expanding circle
var vsound = 0.05; //speed of sound (in some normalized units) 	
var max_radius = bubble_time * vsound; //maximum radius of circles


var Mach_mult = Mach_sup / Mach_sub; // multiplierfor the 2 different Mach numbers
var vsource = Mach_sub * vsound; //speed of source particle
var sourcerd = 5; //radius of source particle
		
var time = range(0.0,15.0);  //creates evenly spaced array
var time = time.map(function(x) {return 1.e3*x ;} ); //time is in seconds now
var xsource = time.map(function(x) {return x * vsource;} ); //position of source at different times


var svg = d3.select("svg");

var canvas = svg
			.attr("width",width)
			.attr("height",height)
			.append("g")
			.attr("transform","translate(20,0)");
					 
var elementRoot = canvas.selectAll("g").data(xsource).enter().append("g");			 

//plot circles for subsonic case
var circles_sub = elementRoot.append("circle")							
					.attr("cx", function(d) { return d; } )
					.attr("cy", ypos)
					.attr("r", 0)
					.attr("fill","none")
					.attr("stroke","black")
						.transition()
						.delay( function(d,i) { return time[i]; } )
						.duration( bubble_time )
						.attr("r", max_radius )
						.remove()
						.ease("linear")

//plot source for subsonic case		
var source_sub = elementRoot.append("circle")
					.attr("cx", function(d) { return d; } )
					.attr("cy", ypos)
					.attr("r", 0)
					.attr("fill","black")
					.transition()
					.delay( function(d,i) { return time[i]; } )
					.duration( 50 )
					.attr("r",sourcerd)
					.remove()

//plot source for supersonic case
var circles_sup = elementRoot.append("circle")							
					.attr("cx", function(d) { return d; } )
					.attr("cy", 2 * ypos)
					.attr("r", 0)
					.attr("fill","none")
					.attr("stroke","black")
					.transition()
						.delay( function(d,i) { return time[i] / Mach_mult; } )
						.duration( bubble_time )
						.attr("r", max_radius )
						.remove()
						.ease("linear")

//plot source forsupersonic case
var source_sup = elementRoot.append("circle")
					.attr("cx", function(d) { return d; } )
					.attr("cy", 2 * ypos)
					.attr("r", 0)
					.attr("fill","black")
					.transition()
						.delay( function(d,i) { return time[i] / Mach_mult; } )
						.duration( 50/Mach_mult )
						.attr("r",sourcerd)
						.remove()

//write labels and boxes for both cases
canvas.append("rect")
			.attr("width", textwidth)
			.attr("height",textheight)
			.attr("x",xpos).attr("y",ypos-textheight/2)
			.attr("fill","steelblue")
canvas.append("rect")
			.attr("width", textwidth)
			.attr("height",textheight)
			.attr("x",xpos).attr("y",2 * ypos-textheight/2)
			.attr("fill","steelblue")
					
canvas.append("text").text("SUBSONIC")
				.attr("x",xpos+32).attr("y",ypos+5)
				.attr("fill","black")
canvas.append("text").text("SUPERSONIC")
				.attr("x",xpos+23).attr("y",2 * ypos+5)
				.attr("fill","black")