How to Calculate Total in XML Publisher Report

declare a variable on top of the group.

<?xdoxslt:set_variable($_XDOCTX, 'TROW_NUM', 0)?>

add another variable inside the loop.

<?xdoxslt:set_variable($_XDOCTX, 'TROW_NUM',
xdoxslt:get_variable($_XDOCTX, 'TROW_NUM') +  COLUMN_NAME)?>

And put the below inside the total field

<?xdoxslt:get_variable($_XDOCTX, 'TROW_NUM')?>