Math Weirdness
in [General]
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From: "Jay Blanchard" on 14 Jul 2008 13:39 I am totally buffaloed by a set of very simple calculations that I am doing; /* calculate total balance with payments and adjustments */ $totalBalance = $acct['BALANCE'] + $adjBalance; echo number_format($totalBalance, 2, '.', '')."\t"; /* calculate total charges */ $totalCharges = $intlLDCharges + $longDistance + $smsCharges + $daCharges + $totalData + $roaming; echo number_format($totalCharges, 2, '.', '')."\t"; /* * calculate difference between total balance and total charges * if the amount matches the ending balance then all is OK * if not calculate the difference */ $totBalDiff = $totalBalance - $totalCharges; if($totBalDiff === $endingBal){ echo "OK\t"; } else { /* what is the difference between the ending balance and the charges? */ $totChargeDiff = $endingBal - $totalCharges; echo number_format($totChargeDiff, 2, '.', '')."\t"; } Each number represented by a variable in all of these calculations has been rounded to 2 decimal points at the point they are generated. For the most part this works just hunky-dory but I have a handful of calcs (out of 300k plus records) that look like this.... $endingBal 0.10 $totalBalance 0.30 $totalCharges 0.20 $totalChargeDiff -0.10 The balance minus the charges does equal the ending balance as it should but it is saying that it doesn't and that there a 20 cent swing (-0.10 is 20 cents different than 0.10). I must be missing something. When I echo out raw data I do not see negative signs. Does anyone have any insight as to what might be happening here?
From: Robert Cummings on 14 Jul 2008 13:55 On Mon, 2008-07-14 at 12:39 -0500, Jay Blanchard wrote: > /* calculate total balance with payments and adjustments */ > $totalBalance = $acct['BALANCE'] + $adjBalance; > echo number_format($totalBalance, 2, '.', '')."\t"; > > /* calculate total charges */ > $totalCharges = $intlLDCharges + $longDistance + $smsCharges + > $daCharges + $totalData + $roaming; > echo number_format($totalCharges, 2, '.', '')."\t"; > > /* > * calculate difference between total balance and total > charges > * if the amount matches the ending balance then all is OK > * if not calculate the difference > */ > $totBalDiff = $totalBalance - $totalCharges; > if($totBalDiff === $endingBal){ > echo "OK\t"; > } else { > /* what is the difference between the ending balance > and > the charges? */ > $totChargeDiff = $endingBal - $totalCharges; > echo number_format($totChargeDiff, 2, '.', '')."\t"; > } What makes you think the problem is in this code? How about doing the following right before the block of code you've provided so that we can actually check the data with what you're using: <?php echo '$acct["BALANCE"]: '.$acct["BALANCE"]."\n"; echo '$adjBalance: '.$adjBalance."\n"; echo '$intlLDCharges: '.$intlLDCharges."\n"; echo '$longDistance: '.$longDistance."\n"; echo '$smsCharges: '.$smsCharges."\n"; echo '$roaming: '.$roaming."\n"; echo '$daCharges: '.$daCharges."\n"; echo '$totalData: '.$totalData."\n"; echo '$endingBal: '.$endingBal."\n"; ?> Cheers, Rob. -- http://www.interjinn.com Application and Templating Framework for PHP
From: "Jay Blanchard" on 14 Jul 2008 14:32 [snip] What makes you think the problem is in this code? How about doing the following right before the block of code you've provided so that we can actually check the data with what you're using: <?php echo '$acct["BALANCE"]: '.$acct["BALANCE"]."\n"; echo '$adjBalance: '.$adjBalance."\n"; echo '$intlLDCharges: '.$intlLDCharges."\n"; echo '$longDistance: '.$longDistance."\n"; echo '$smsCharges: '.$smsCharges."\n"; echo '$roaming: '.$roaming."\n"; echo '$daCharges: '.$daCharges."\n"; echo '$totalData: '.$totalData."\n"; echo '$endingBal: '.$endingBal."\n"; ?> [/snip] $adjBalance: 0 $intlLDCharges: 0.2 $longDistance: 0 $smsCharges: 0 $roaming: 0 $daCharges: 0 $totalData: 0 $endingBal: 0.1 I had done this looking for special characters or negative signs.
From: Robert Cummings on 14 Jul 2008 15:04 On Mon, 2008-07-14 at 12:39 -0500, Jay Blanchard wrote: > I am totally buffaloed by a set of very simple calculations that I am > doing; > > /* calculate total balance with payments and adjustments */ > $totalBalance = $acct['BALANCE'] + $adjBalance; > echo number_format($totalBalance, 2, '.', '')."\t"; > > /* calculate total charges */ > $totalCharges = $intlLDCharges + $longDistance + $smsCharges + > $daCharges + $totalData + $roaming; > echo number_format($totalCharges, 2, '.', '')."\t"; > > /* > * calculate difference between total balance and total charges > * if the amount matches the ending balance then all is OK > * if not calculate the difference > */ > $totBalDiff = $totalBalance - $totalCharges; > if($totBalDiff === $endingBal){ > echo "OK\t"; > } else { > /* what is the difference between the ending balance and > the charges? */ > $totChargeDiff = $endingBal - $totalCharges; > echo number_format($totChargeDiff, 2, '.', '')."\t"; > } > > Each number represented by a variable in all of these calculations has > been rounded to 2 decimal points at the point they are generated. For > the most part this works just hunky-dory but I have a handful of calcs > (out of 300k plus records) that look like this.... > > $endingBal 0.10 > $totalBalance 0.30 > $totalCharges 0.20 > $totalChargeDiff -0.10 > > The balance minus the charges does equal the ending balance as it should > but it is saying that it doesn't and that there a 20 cent swing (-0.10 > is 20 cents different than 0.10). > > I must be missing something. When I echo out raw data I do not see > negative signs. Does anyone have any insight as to what might be > happening here? >From whence do you conjure $endingBal? Most likely this is just a floating point imprecision problem. In otherwords, you need a small delta of error when doing the following comparison: if( $totBalDiff === $endingBal ) Remember, floating point numbers do not always store perfectly. So you want something like: if( abs( $totalBalDiff - $endingBal ) > .000001 ) Also that last echo: echo number_format($totChargeDiff, 2, '.', '') Was calculated with: $totChargeDiff = $endingBal - $totalCharges; Whereas the initial conditional checks: $totBalDiff === $endingBal And $totBalDiff was calculated as: $totBalDiff = $totalBalance - $totalCharges; So again... from whence do you conjure $endingBal? :) Cheers, Rob. -- http://www.interjinn.com Application and Templating Framework for PHP
From: "Jay Blanchard" on 14 Jul 2008 15:12
[snip] So again... from whence do you conjure $endingBal? :) [/snip] $endingBal is conjured from the database tracking the account balance. For any 24 hour period the beginning and ending balance for subsequent days is the same unless adjustments or payments have been made to the account in that period. 2:35 AM balance becomes the ending balance for the previous day and becomes the beginning balance for the day we are beginning. |