Magento: Find subcategories for a particular root category

We can use the below code to find all child categories for a particular root category in Magento




<?php

   

   //get category model




    $category_model = Mage::getModel('catalog/category'); 

 //$categoryid for which we have to find the child categories (root category id   or other parent category id)




    $_category = $category_model->load($categoryid); 

 //array that contains all child categories id

        

$all_child_categories = $category_model->getResource()->getAllChildren($_category);




foreach($all_child_categories as $childcatId)

{

   echo $childcatId; //// here you get child categories id

}




?>