未定义的索引：CodeIgniter中的alamat

i have error with in my view undefined index alamat in view code. i hope you can help me how solve this error?

view code

    <tr>
    <td valign="top">Alamat</td>
    <td><input type="text" name="alamat" class="text" value="<?php echo set_value('alamat')? set_value('alamat'):$siswa['alamat'];?>"/>
    <?php echo form_error('alamat');?></td>
    </tr>

in view code error undefined alamat. write code set_value('alamat) it true or false? controller code

function update($id=1)
            {
                /* set common properties */ 
                $data['title'] = 'Update siswa';
                $this->load->library('form_validation');
                /* set validation properties */
                    $this->_set_rules();
                    $data['action']=('siswa/update/'.$id);

                    //run validation
                    if ($this->form_validation->run() === FALSE) {
                        $data['message']='';

                        $data['siswa'] = $this->siswa_model->get_by_id($id)->row_array();
                        if (isset($_POST['jenis_kelamin'])) {
                            $_POST['jenis_kelamin'] = strtoupper($data['siswa']['jenis_kelamin']);
                        }
                        if (isset($_POST['tanggal_lahir'])) {
                            $data['siswa']['tanggal_lahir'] = date('d-m-Y',strtotime($data['siswa']['tanggal_lahir']));
                        }

                        //set common properties
                        $data['title']='Update siswa';
                        $data['message']='';

                    }
                    else
                    {
                        //save data
                        $id = $this->input->post('id');
                        $siswa=array( 'id'=>$id,
                            'nama'=>$this->input->post('nama'),
                            'alamat'=>$this->input->post('alamat'),
                            'jenis_kelamin'=>$this->input->post('jenis_kelamin'),
                            'tanggal_lahir'=>date('Y-m-d', strtotime($this->input->post('tanggal_lahir'))));
                        $this->siswa_model->update($id,$siswa);
                        $data['siswa'] = $this->siswa_model->get_by_id($id)->row_array;

                        //set user message;
                        $data['message']='update siswa success';
                    }
                    $data['link_back']= anchor('siswa/index/','Lihat Daftar Siswa',array('class'=>'back'));

                    //load view
                    $this->load->view('siswaEdit',$data);
            }       

Instead of using <?php echo set_value('alamat')? set_value('alamat'):$siswa['alamat'];?> just try this

<?php echo set_value('alamat'); ?>