从html页面获取数据并使用php和tcpdf将显示的输出转换为pdf

i got an error of undefined index a b d1 d2 when converting to pdf file and dept column is not displayed here is the code thankyou

<?php  
 function fetch_data()  
 {  
      $output = '';  
      $connect = mysqli_connect("localhost", "root", "", "aeis");

    $a=$_POST['a'];
    $b=$_POST['b'];
    $from=date('Y-m-d',strtotime($_POST['d1']));
    $to=date('Y-m-d',strtotime($_POST['d2']));

$sql = "SELECT t1.fid,s1.name,s1.dept,t1.date,t1.board,t1.time FROM sample s1,adinvglltn t1 where t1.fid=s1.fid and dept='$a'and board='$b' and date between '$from' and '$to' ORDER BY date ASC";

      $result = mysqli_query($connect, $sql); 

      while($row = mysqli_fetch_array($result))  
      {       
      $output .= '<tr>  

                <td><input type="text" value="'.$row["fid"].'"></td>  
               <td><input type="text" value="'.$row["name"].'"></td>  
               <td<input type="text" value="'.$row["dept"].'"></td>  
               <td><input type="text" value="'.$row["date"].'"></td>  
               <td><input type="text" value="'.$row["board"].'"></td>  
               <td><input type="text" value="'.$row["time"].'"></td>            

                     </tr>';

      }  
      return $output;  
 }  
 if(isset($_POST["create_pdf"]))  
 {  ob_start();
      require_once('tcpdf/tcpdf.php');  
      $obj_pdf = new TCPDF('P', PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', false);  
      $obj_pdf->SetCreator(PDF_CREATOR);  
      $obj_pdf->SetTitle("Export HTML Table data to PDF ");  
      $obj_pdf->SetHeaderData('', '', PDF_HEADER_TITLE, PDF_HEADER_STRING);  
      $obj_pdf->setHeaderFont(Array(PDF_FONT_NAME_MAIN, '', PDF_FONT_SIZE_MAIN));  
      $obj_pdf->setFooterFont(Array(PDF_FONT_NAME_DATA, '', PDF_FONT_SIZE_DATA));  
      $obj_pdf->SetDefaultMonospacedFont('helvetica');  
      $obj_pdf->SetFooterMargin(PDF_MARGIN_FOOTER);  
      $obj_pdf->SetMargins(PDF_MARGIN_LEFT, '5', PDF_MARGIN_RIGHT);  
      $obj_pdf->setPrintHeader(false);  
      $obj_pdf->setPrintFooter(false);  
      $obj_pdf->SetAutoPageBreak(TRUE, 10);  
      $obj_pdf->SetFont('helvetica', '', 12);  
      $obj_pdf->AddPage();  
      $content = '';  
      $content .= '  
      <h3 align="center">Export HTML Table data to PDF </h3><br /><br />  
      <table border="1" cellspacing="0" cellpadding="5">  
           <tr>  
                <th width="10%">FID</th>  
                <th width="40%">NAME</th>  
                <th width="40%">DEPT</th>  
                <th width="10%">DATE</th>  
                 <th width="10%">BOARD</th>  
                 <th width="10%">TIME</th>  
           </tr>  
      ';  
      $content .= fetch_data();  
      $content .= '</table>';  
      $obj_pdf->writeHTML($content);
        ob_end_clean();   
      $obj_pdf->Output($_SERVER['DOCUMENT_ROOT'] . 'sample.pdf', 'F');  
 }  
 ?>  
 <!DOCTYPE html>  
 <html>  
      <head>  
           <title> Export HTML Table data to PDF </title>  
           <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" />            
      </head>  
      <body>  
           <br /><br />  
           <div class="container" style="width:700px;">  
                <h3 align="center">Export HTML Table data to PDF </h3><br />  
                <div class="table-responsive">  
                     <table class="table table-bordered">  
                          <tr>  
                                 <th width="5%">FID</th>  
                         <th width="30%">NAME</th>  
                         <th width="10%">DEPT</th>  
                         <th width="45%">DATE</th>
                            <th width="45%">BOARD</th>   
                            <th width="45%">TIME</th>   
                          </tr>  
                     <?php  

                     echo fetch_data();  
                     ?>  
                     </table>  
                     <br />  
                     <form method="post">  
                          <input type="submit" name="create_pdf" class="btn btn-danger" value="Create PDF" />  
                     </form>  
                </div>  
           </div>  
      </body>  
 </html

i got an tcpdf error please help me to solve this problem.actually i send data from html page to php page the the output is displayed after that i want to create a pdf for the output. php variables are not taken when converting to pdf