Once a promising music student at Juilliard, Nathaniel Ayers was schizophrenic and homeless, playing violin on the streets of LA, when columnist Steve Lopez began writing about him in the Los Angeles Times in 2005. I wasn’t sure what to expect from this screen adaptation of Lopez’s book: it was scripted by mushmonger Susannah Grant (In Her Shoes), directed by the tough-minded Joe Wright (Atonement), produced by the lefty-activist outfit Participant Productions (Charlie Wilson’s War), and released (in halting fashion) by the crowd-pleasing Dreamworks SKG. As it turns out, the movie is a strikingly downbeat look at the lives of the homeless, anchored in scary, dismal, and frequently moving scenes at a local shelter. The setup promises redemption and triumph, and the movie delivers, in a way. But it also looks honestly at the intractable problems of dealing with the mentally ill who roam our streets. With Catherine Keener. PG-13, 109 min.