Cultural assimilation is a specialty for Mira Nair, the India-born, Manhattan-based director who found he right balance in Mississippi Masala and Monsoon Wedding and soars with her film version of Jhumpa Lahiri’s novel The Namesake . In Calcutta, circa the 1970s, Ashoke (Irrfan Khan) and Ashima (Tabu) agree o an arranged marriage and to ting their new lives in Manhattan. It’s a struggle. The birth of their son, Nikhil, who is given the pet name Gogol, after the Russian author Ashoke reveres, intensifies the cultural clash. The grown Gogol, played with ferocity and feeling by Kal Penn, of Harold and Kumar fame, turns his back on everything Indian, and not just by taking up with a blond socialite (Jacinda Barrett). Gogol has identity problems, not solvable when he leaves the blonde for the Bengali beauty Moushumi (a zesty Zuleikha Robinson). It takes a family tragedy to give Gogol a sense of himself and his namesake. Nair tries to shoehorn too much of a big novel into a small two-hour movie. But her ardor for the material matches her ambition. This is a generational family saga everyone can relate to, and Nair gives it her special magic.