user-defined function

Anon

to make my question simpler, lets say I want the user to input a mathematical expression of X and Y, and a value for x,y and make php calculate the outcome of the expression,

so, if the user inputs : f(x,y) = sin(x)+cos(y) + x + y
PHP will plug-in the x,y values and yield the answer.

in other words, how would I make php evaluate a string as a mathematical expression(or a PHP expression). ???
help me !

Anon

i would use a form and set all the appropriate text inputs to variables which upon submission of the form would pass the variables through the equation you have written.

a very rough example

<? if ($submit) (

// process the equation ( how does one code sin($x)+cos($y) + $x + $y in php?)

$answer = sin($x)+cos($y) + $x + $y

// print the answer
echo "$answer";

} else { ?>

// print the form
<form ... action="<? echo "$PHP_SELF"; ?>">
<input type="text" name="x">
<input type="text" name="y">
etc...
</form>
<? } ?>

This will pass the variables from the form into the equation... how to write the actual equation in PHP is beyond me.
I have no idea how to code the actual equation but this is the logic of how the web page would act... although I do want to learn how to write mathematical equations with PHP someday... anyone have suggestions?
Also, have you thought of using XML for this?

Anon

when the user types-in the equation in the text field, and it gets assigned to a variable, .. php will trat that variable as a text string :

example:
$x = 1
$y = 4

$Z = $function3
/ this will evaluate as ZERO, because the variable $function which the user submitted in the form is trated as a text string, with numerical value of Zero, .. */

how would I make php evaluate: $function*3

as ((sin(1)+cos(4) + 1 + 4 )*3) ???

lexzeus

Hi there ...

try to use eval :

<?
$x=10;
$y=100;

eval("\$f = sin(\$x) * sin (\$y) + \$x + $y ; ");

print $f;
?>

now, $f should be : sin(x)*sin(y)+x+y ....

LexZEUS
http://lexzeus.tripod.com/

Anon

oh man, thanks a million, this really worked

I'm working on a php script for my differential equations class, finding solutions by numerical approximations.
http://www.njneer.com

Anon

okay, eval(), (a statement not a function), evaluates a string as if it was PHP code (so be careful if users are to enter the argument in an HTML form!!).
I found that it cant really evaluate arithmetica expressions,
in my case, (http://www.njneer.com/math/math.htm) the user will have to type a mathematical function the same way its done in PHP (like adding $ before the variables x,y ) .. also, instead of typing x² , it would have to be pow ($x, 2).

we can work on that, by manipulating the string the user enters, .. using string functions to add the $ before X,Y , we can also use regular expressions to evaluate x^y as pow (x, y) in other words, write an arithmetic expression parser for PHP.

is there already one? .. I think that would be an interesting project for me.

Mahmoud Arram
soph, CoE
NJIT.edu