note 96762 added to ref.math
| From: | dmautz at gmail dot com | Date: | Mon, 15 Mar 2010 03:57:28 +0000 |
| Subject: | note 96762 added to ref.math | ||
| Groups: | php.notes | ||
| Request: | Send a blank email to php-notes+get-167024@lists.php.net to get a copy of this message | ||
Here are some functions to determine the loan amount, payment amount, number of payments, and
interest rate on a mortgage when 3 of the 4 variables are know.
function find_amount($num_payments,$payment,$int_rate)
{
$int = $int_rate/1200;
$int1 = 1+$int;
$r1 = pow($int1, $num_payments);
$amount= $payment*($r1-1)/($int*$r1);
$amount= number_format($loan, 2, '.', '');
return $amount;
}
function find_num_payments($amount,$payment,$int_rate)
{
int = $int_rate/1200;
$num_payments = -log(1-($int*($amount/$payment)))/log(1+($int));
$num_payments = round($num_payments);
return $num_payments;
}
function find_int_rate($amount,$num_payments,$payment)
{
$min_rate = 0;
$max_rate = 100;
while ($min_rate < $max_rate - 0.0001)
{
$mid_rate = ($min_rate + $max_rate) / 2; // Divide by 2 to find midpoint
$int = $mid_rate/1200;
$int1 = 1+$int;
$r1 = pow($int1, $num_payments);
$guessed_pmt = $amount*($int*$r1)/($r1-1);
if ($guessed_pmt > $payment)
{
$max_rate = $mid_rate; // current rate is new maximum
}else{
$min_rate = $mid_rate; // current rate is new minimum
}
}
$int_rate = number_format($mid_rate, 2, '.', '');
return $int_rate
}
function find_payment($amount,$num_payments,$int_rate)
{
$int = $int_rate/1200;
$int1 = 1+$int;
$r1 = pow($int1, $num_payments);
$payment = $loan*($int*$r1)/($r1-1);
$payment = number_format($payment, 2, '.', '');
return $payment;
}
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