alejandrofloresm

<?php
/**
 * Returns the inverse of the standard normal cumulative distribution. 
 * The distribution has a mean of zero and a standard deviation of one.
 * Resources: 
 *   http://board.phpbuilder.com/showthread.php?10367349-PHP-NORMSINV
 *   http://www.source-code.biz/snippets/vbasic/9.htm
 * @param  integer $week number of week
 * @return float       sales
 */

kmpm

/// Original C++ implementation found at http://www.wilmott.com/messageview.cfm?catid=10&threadid=38771
/// C# implementation found at http://weblogs.asp.net/esanchez/archive/2010/07/29/a-quick-and-dirty-implementation-of-excel-norminv-function-in-c.aspx
/*
 *     Compute the quantile function for the normal distribution.
 *
 *     For small to moderate probabilities, algorithm referenced
 *     below is used to obtain an initial approximation which is
 *     polished with a final Newton step.
 *
 *     For very large arguments, an algorithm of Wichura is used.