function clearForm() {
	$('principal').value = "";
	$('interest_rate').value = "";
	$('amortization_period').value = "";
}

function validateMortgagePayments() {

	var ret = true;
	if ( !IsNumeric( $('principal').value ) )
	{
		alert('Please enter a valid principal amount.');
		ret = false;
	}
	else if ( !IsNumeric( $('interest_rate').value ) )
	{
		alert('Please enter a valid interest rate.');
		ret = false;
	}
	else if ( !IsNumeric( $('amortization_period').value ) )
	{
		alert('Please enter a valid amortization period.');
		ret = false;
	}	
	return ret;
}

function IsNumeric(sText)
{

	var ValidChars = "0123456789.";
	var IsNumber=true;
	var Char;
	if ( sText.length == 0 )
		return false;
		
	for (i = 0; i < sText.length && IsNumber == true; i++) 
	{ 
		Char = sText.charAt(i); 
		if (ValidChars.indexOf(Char) == -1) 
		{
			IsNumber = false;
		}
	}
	return IsNumber;  
 }