math - Calculating interest rate in PHP with converted Excel RATE Function -


i'm having issue - 1 example works , next doesn't

here's code

define('financial_max_iterations', 128); define('financial_precision', 1.0e-08);  function rate($nper, $pmt, $pv, $fv = 0.0, $type = 0, $guess = 0.1) {  $rate = $guess;  if (abs($rate) < financial_precision) {      $y = $pv * (1 + $nper * $rate) + $pmt * (1 + $rate * $type) * $nper + $fv;  } else {      $f = exp($nper * log(1 + $rate));      $y = $pv * $f + $pmt * (1 / $rate + $type) * ($f - 1) + $fv;  }  $y0 = $pv + $pmt * $nper + $fv;  $y1 = $pv * $f + $pmt * (1 / $rate + $type) * ($f - 1) + $fv;   // find root secant method  $i  = $x0 = 0.0;  $x1 = $rate;  while ((abs($y0 - $y1) > financial_precision) && ($i < financial_max_iterations)) {      $rate = ($y1 * $x0 - $y0 * $x1) / ($y1 - $y0);      $x0 = $x1;      $x1 = $rate;     if (($nper * abs($pmt)) > ($pv - $fv))         $x1 = abs($x1);      if (abs($rate) < financial_precision) {          $y = $pv * (1 + $nper * $rate) + $pmt * (1 + $rate * $type) * $nper + $fv;      } else {          $f = exp($nper * log(1 + $rate));          $y = $pv * $f + $pmt * (1 / $rate + $type) * ($f - 1) + $fv;      }       $y0 = $y1;      $y1 = $y;      ++$i;  }   $rate = abs(round($rate*100,5));  return $rate;   } // function rate()

and examples rate(60,-1338.88,274775,0,0,0.03200); // works - returns 3.40321

rate(60,-2415.44,448925,0,0,0.04150); // doesn't work - returns 3.16288 when should 4.32

any ideas? i've tried 4-5 pieces of code similar , 1 seems give me best results, though aren't consistent. feel code works, because how give me 1 correct result , rest aren't??

p.s: i'm newb @ posting here, i've been reading site 5 years though - hope thorough enough ;)

similar question, info, still doesn't solve problem secant method of iteration php

another question, still doesn't need... calculating interest rate in php


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