// calculate function etc for loan payment calculator
function calculate() {
    // Get the user's input from the form. Assume it is all valid.
    // Convert interest from a percentage to a decimal, and convert from
    // an annual rate to a monthly rate. Convert payment period in years
    // to the number of monthly payments.
    var principal = document.loandata.principal.value;
    var interest = document.loandata.interest.value / 100 / 12;
    var payments = document.loandata.months.value;
	// check that a comma has not been entered, if it has remove it
	var iscomma = document.loandata.principal.value.indexOf(",");
    if (iscomma > -1) {
	  var s1 = document.loandata.principal.value.slice(0, iscomma);
	  var s2 = document.loandata.principal.value.slice(iscomma + 1, principal.length);
  	  var s3 = (s1 + s2);
	  principal = eval(s3);
	} 
    // Now compute the monthly payment figure, using esoteric math.
    var x = Math.pow(1 + interest, payments);
    var monthly = (principal*x*interest)/(x-1);

    // Check that the result is a finite number. If so, display the results
    if (!isNaN(monthly) && 
        (monthly != Number.POSITIVE_INFINITY) &&
        (monthly != Number.NEGATIVE_INFINITY)) {

        document.loandata.payment.value = round(monthly);
        document.loandata.total.value = round(monthly * payments);
        document.loandata.totalinterest.value = 
            round((monthly * payments) - principal);
    }
    // Otherwise, the user's input was probably invalid, so don't
    // display anything.
    else {
        document.loandata.payment.value = "";
        document.loandata.total.value = "";
        document.loandata.totalinterest.value = "";
    }
}

// This simple method rounds a number to two decimal places.
function round(x) {
  return Math.round(x*100)/100;
}