Re Index programmatically Magento::

>> if you want to reindex "Category Products" only then you can do as follows:-
         $process = Mage::getModel('index/process')->load(6);
         $process->reindexAll();
       
         If you want to reindex all data then you can loop through these indices and then reindex them:-
         for ($i = 1; $i <= 9; $i++) {
             $process = Mage::getModel('index/process')->load($i);
             $process->reindexAll();
         }