PHP - latex format of function with regex - php

Question

Is it possible to write a regex which would take input like 'sqrt(2 * (2+2)) + sin(pi/6)' and transform it into '\sqrt{2 \cdot (2+2)} + \sin(\pi/6)'?
The problem is the 'sqrt' and parentheses in it. It is obvious I can't simply use something like this:
/sqrt\((.?)\)/ -> \\sqrt{$1}
because this code would create something like this '\sqrt{2 \cdot (2+2)) + \sin(\pi/6}'.

Answer 1

My solution: it simply go throw the string converted to char array and tests if a current substring starts with $latex, if it does second for-cycle go from this point in different direction and by parentheses decides where the function starts and ends. (startsWith function)
Code:
public static function formatFunction($function, $latex, $input) {
$input = preg_replace("/" . $function . "\(/", $latex . "{", $input);
$arr = str_split($input);
$inGap = false;
$gap = 0;
for ($i = count($arr) - 1; $i >= 0; $i--) {
if (startsWith(substr($input, $i), $latex)) {
for ($x = $i; $x < count($arr); $x++) {
if ($arr[$x] == "(" || $arr[$x] == "{") { $gap++; $inGap = true; }
else if ($arr[$x] == ")" || $arr[$x] == "}") { $gap--; }
if ($inGap && $gap == 0) {
$arr[$x] = "}";
$inGap = false;
break;
}
}
}
$gap = 0;
}
return implode($arr);
}
Use:
self::formatFunction("sqrt", "\\sqrt",
"sqrt(25 + sqrt(16 - sqrt(49)) + (7 + 1)) + sin(pi/2)");
Output:
\sqrt{25+\sqrt{16-\sqrt{49}}+(7+1)}+\sin (\pi/2)
Note: sin and pi aren't formated by this code, it's only str_replace function...

Answer 2

In general, no regular expression can effectively handle nested parentheses. Sorry to be the bearer of bad news! The MathJAX parser library can interpret LaTeX equations and you could probably add a custom output routine to do what you want.
For TeX questions, you can also try http://tex.stackexchange.com .

Answer 3

Some time ago i soved a similar problem in such way. Maybe it will be helpful for you
$str = 'sqrt((2 * (2+2)) + sin(pi/(6+7)))';
$from = []; // parentheses content
$to = []; // patterns for replace #<number>
$brackets = [['(', ')'], ['{', '}'], ['[', ']']]; // new parentheses for every level
$level = 0;
$count = 1; // count or replace made
while($count) {
$str = preg_replace_callback('(\(([^()]+)\))',
function ($m) use (&$to, &$from, $brackets, $level) {
array_unshift($to, $brackets[$level][0] . $m[1] . $brackets[$level][1]);
$i = '#' . (count($to)-1); // pattern for future replace.
// here it '#1', '#2'.
// Make it so they will be unique
array_unshift($from, $i);
return $i; }, $str, -1, $count);
$level++;
}
echo str_replace($from, $to, $str); // return content back
// sqrt[{2 * (2+2)} + sin{pi/(6+7)}]
I forgot all details, but it, seems, works