Dynamic calculation loop problem

cichlid

I'm trying to do perform a series of calculations based on some initial user input, but am, frankly, a little baffled and would really appreciate some pointers, please?!

What I'm trying to do, is take some user data (initial level, weekly increase and frequency) and then perform a set number of calculations based on the frequency, ie. 52 calculations, one for each week.

This might be a bit tricky to explain, but at the start of the loop, week 1 of $frequency, the initial_level is (for example) 11, but this changes as a result of the calculation. I want to pass the new result ($calculation) to the next calculation.

So, for example, if in week 1, the level is 11, it might change to 10.1 in week 2, 9.8 in week 3 and so on. Basically, I'm trying to predict the level after 52 weeks, based on 52 repetitions of the calculation.

// Initial level from user
$initial_level = "11";
$weekly_increase = "4";
$frequency = "52"; // weekly


// Set up loop
$actions = 1;
$calculation = $initial_level;

while ($actions <= $frequency) {
	// Perform calculation
	$calculation =  ( ( .25 * $calculation) + $weekly_increase) / .25;

// Debugging
print("$actions : $calculation =  ( ( .25 * $calculation) + $weekly_increase) / .25<br/>");

// Increment loop for next water change
$actions++;
}

However, while I can get the loop to run 52 times, I can't get it to pass the result of the calculation to the next calculation (ie. the result of week 1 ($calculation) becomes the $calculation value used in the calculation for week 2.

Apologies if I've not explained this very clearly. If I actually explained the calculation, it would probably only confuse you even more!

Any input would be extremely gratefully received.

Many thanks!

Installer

I really don't know what you mean by "I can't get it to pass the result of the calculation to the next calculation". Of course it's being "passed"; after you assign to it the value of the calculation, that's the value it has on the next iteration, and so on. I don't know if your formula is constructed correctly or not, but the value of "$calculation" is changed each time through the loop. It goes from 27, 43, 59, up to 843 after the 52nd iteration.

laserlight

I can't get it to pass the result of the calculation to the next calculation (ie. the result of week 1 ($calculation) becomes the $calculation value used in the calculation for week 2.

It doesnt look like you should have that problem.

// Initial level from user
$initial_level = 11;
$weekly_increase = 4;
$frequency = 52; // weekly

for ($i = 0; $i < $frequency; $i++) {
	$initial_level += $weekly_increase * 4;
}
//now $initial_level contains the final result of the calculations

cichlid

Many thanks for the speedy response! Sorry I didn't make this clearer.

At the moment, the first few lines of the output produce this:

1 : 27 = ( ( .25 27) + 4) / .25
2 : 43 = ( ( .25 43) + 4) / .25
3 : 59 = ( ( .25 * 59) + 4) / .25

What I want them to do is this:

1: 43 = ( ( .25 27) + 4) / .25
2: 59 = ( ( .25 43) + 4) / .25
3: 75 = ( ( .25 * 59) + 4) / .25

At the moment, each calculation uses the same value in two places, which is wrong.

Much thanks!

laserlight

Um, I think that that is a bug with your debugging test, not a bug with your actual script.
Just set
$temp = $calculation;
before you perform the calculation, then:
print "$actions : $calculation = ( ( .25 * $temp) + $weekly_increase) / .25<br/>";

cichlid

Laserlight! You're a genius!

Thank you very much indeed!

🙂