var principle;
var term;
var rate;
var monthlyInterest;
var numPayments;
var payment;
var intrst

function setGlobals () {
	principle = document.form.principle.value;
	term = document.form.term.value;
	rate = document.form.interest.value / 100;
	monthlyInterest = (rate / 12);
	numPayments = (12 * term);
	intrst = exp ((1 + monthlyInterest), numPayments);
	return true;
}

function calculatePayment (form) {
	setGlobals();
	payment = (principle * intrst * monthlyInterest) / (intrst - 1);
	payment = Math.round(payment*Math.pow(10,2)) / Math.pow(10,2);
	document.form.payment.value = payment;
	return true;
}

function clearForm (form) {
	document.form.principle.value= "100000";
	document.form.term.value= "30";
	document.form.interest.value= "7";
	document.form.payment.value= "";
}

function drawGraph () {
	//B_n = A(1 + i)^n - (P/i)[(1 + i)^n - 1]
	//var A = document.form.principle.value;
	//var interest = ((document.form.interest.value / 100) / 12);
	//var n;
	//var P = payment;
	//document.write(P);
	//document.write("made it inside drawGraph()");
	var debt_imgs = new Array();
	var equity_imgs = new Array();
	var d_height = 100;
	for (var i = 0; i < term; i++) 
	{
		debt_imgs[i] = new Image(4, d_height);
		debt_imgs[i].src = 'img/debt_bar.gif';
		d_height -= 3;
	}
	var e_height = 0;
	for (var j = 0; j < term; j++) 
	{
		e_height += 3;
		equity_imgs[j] = new Image(4, e_height);
		equity_imgs[j].src = 'img/equity_bar.gif';
	}
	for (var k = 0; k < term; k++) 
	{
		document.write("<img src='img/debt_bar.gif' width='" + debt_imgs[k].width + "' height='" + debt_imgs[k].height + "' /><img src='img/equity_bar.gif' width='" + equity_imgs[k].width +"' height='" + equity_imgs[k].height + "' />");
	}
	return true;
}

function exp (a, b) {
	var c = a;
	while (b >= 0 )
	{
		c = c * a;
		--b;
	}
	return c;
}