How to output mathematical formulas in php code

使用google的接口显示数学公式

单行公式  （推荐学习：PHP视频教程）

<img  src="http://latex.codecogs.com/gif.latex?$(a_{1})^2+(a_{3})^2\geq%202(a_{2})^2$" / alt="How to output mathematical formulas in php code" >

多行公式

<img  src="http://latex.codecogs.com/gif.latex?$$%20\left\{%20\begin{aligned}%200\leq%20x\leq%202%20\\%200\leq%20y\leq%202\\%20\end{aligned}%20\right.%20$$" / alt="How to output mathematical formulas in php code" >

$str='$$ \left\{
                   \begin{aligned}
                   x^2+3y^2=3 \\
                   y=k(x-1)\\
                   \end{aligned}
                   \right.
        $$';
    //将$$转化为$$
    $str=str_replace("$$", "$", $str);
    // dd($str);
    $pattern='/\$(.*)\$/Us';//只能识别$$  $$
    preg_match_all($pattern,$str,$matches);
    $arr_split=preg_split($pattern,$str);
    //dd($arr_split);
    // dd($matches);
    $count=count($matches[1]);
    $str_new="";
    for($i=0;$i<count($matches[1]);$i++){
        //$arr_replace[]=&#39;<img  src="http://latex.codecogs.com/gif.latex?&#39;.$matches[1][$i].&#39;" / alt="How to output mathematical formulas in php code" >&#39;;
        $matches_str=$matches[1][$i];
        // dd($str);
        //先把\\n转换成\\\n
        $matches_str=str_replace("\\\n", "\\\\\n", $matches_str);
        // dd($matches_str);
        $matches_str=preg_replace(&#39;/\s*/&#39;, &#39;&#39;, $matches_str);
        // dd($matches_str);
        $str_new.=$arr_split[$i];
        $str_new.=&#39;<img  src="http://latex.codecogs.com/gif.latex?&#39;.$matches_str.&#39;" / alt="How to output mathematical formulas in php code" >&#39;;
    }
    if($count>0){
        echo $str_new;
    }else{
        echo $str;
    }

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