Write SQL query to solve given problem: What is the ratio of Asian male graduates to Asian female graduates from Harvard University in 2013?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(CASE WHEN T2.Gender = 'M' THEN T2.grad_cohort ELSE 0 END) AS REAL) / SUM(CASE WHEN T2.Gender = 'F' THEN T2.grad_cohort ELSE 0 END) FROM institution_details AS T1 INNER JOIN institution_grads AS T2 ON T1.unitid = T2.unitid WHERE T1.chronname = 'Harvard University' AND T2.year = 2013 AND T2.race = 'A'