Magento create invoice programmatically

How to create invoice for order in magento

$order = Mage::getModel('sales/order')->loadByIncrementId([order_id]);



if(!$order->canInvoice())

{

Mage::throwException(Mage::helper('core')->__('Cannot create an invoice.'));

}



$invoice = Mage::getModel('sales/service_order', $order)->prepareInvoice();



$invoice->setTransactionId([last_trans_id]);



$invoice->setRequestedCaptureCase(Mage_Sales_Model_Order_Invoice::CAPTURE_ONLINE);



$invoice->register();



$transactionSave = Mage::getModel('core/resource_transaction')

                                              ->addObject($invoice)

                                              ->addObject($invoice->getOrder());



$transactionSave->save();