PureMisery

01-02-2006, 06:58 AM

Is there a way to get php to solve for a variable?

Ex,

1.1x=110

output to screen would be what x is

Ex,

1.1x=110

output to screen would be what x is

View Full Version : Algebra

PureMisery

01-02-2006, 06:58 AM

Is there a way to get php to solve for a variable?

Ex,

1.1x=110

output to screen would be what x is

Ex,

1.1x=110

output to screen would be what x is

ralph l mayo

01-02-2006, 08:46 AM

Brute force? I'm pretty sure that's how the fancy calculators do it.

function solveForX($equation, $answer, $min = null, $max = null)

{

$min = ($min == null) ? -mt_getrandmax() : $min;

$max = ($max == null) ? mt_getrandmax() : $max;

$last['guess'] = null;

while (true)

{

eval('$attempt = ' . str_replace('x', ($guess = mt_rand($min, $max)), $equation) . ';');

if ($attempt == $answer)

{

return($guess);

}

if ($last['guess'] != null)

{

$diff = abs($answer - $attempt);

if ($diff > $last['diff'])

{

if ($guess > $last['guess'])

{

$max = $guess - 1;

}

else

{

$min = $guess + 1;

}

}

}

$last['guess'] = $guess;

$last['diff'] = abs($answer - $attempt);

}

}

echo solveForX('x+(x*.1)', 110);

Note this is oversimplified and will fall into infinite loops on discontinuous functions and functions with noninteger answers. The latter problem is pretty easily resolvable, the former maybe not so much.

Also, it'd probably be neater if it was refactored to use recursion, another exercise I'll leave to the reader. :p

function solveForX($equation, $answer, $min = null, $max = null)

{

$min = ($min == null) ? -mt_getrandmax() : $min;

$max = ($max == null) ? mt_getrandmax() : $max;

$last['guess'] = null;

while (true)

{

eval('$attempt = ' . str_replace('x', ($guess = mt_rand($min, $max)), $equation) . ';');

if ($attempt == $answer)

{

return($guess);

}

if ($last['guess'] != null)

{

$diff = abs($answer - $attempt);

if ($diff > $last['diff'])

{

if ($guess > $last['guess'])

{

$max = $guess - 1;

}

else

{

$min = $guess + 1;

}

}

}

$last['guess'] = $guess;

$last['diff'] = abs($answer - $attempt);

}

}

echo solveForX('x+(x*.1)', 110);

Note this is oversimplified and will fall into infinite loops on discontinuous functions and functions with noninteger answers. The latter problem is pretty easily resolvable, the former maybe not so much.

Also, it'd probably be neater if it was refactored to use recursion, another exercise I'll leave to the reader. :p

Kurashu

01-02-2006, 08:45 PM

There's some good classes that help handle this.

http://www.phpclasses.org/browse/class/65.html

Check there for some.

http://www.phpclasses.org/browse/class/65.html

Check there for some.

PureMisery

01-03-2006, 05:12 AM

There's some good classes that help handle this.

http://www.phpclasses.org/browse/class/65.html

Check there for some.

Thanks, I'll go look around there now.

<---edit--->

I found one that I think will do what I need. But how do use the files?

http://www.phpclasses.org/browse/class/65.html

Check there for some.

Thanks, I'll go look around there now.

<---edit--->

I found one that I think will do what I need. But how do use the files?

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