updated doc strings.  added test for threshold
updated doc strings.  added test for threshold

kidaa/pyamg,pyamg/pyamg,kidaa/pyamg,pyamg/pyamg,huahbo/pyamg,kidaa/pyamg,huahbo/pyamg,huahbo/pyamg,huahbo/pyamg,pyamg/pyamg,kidaa/pyamg