The Amazing Rob Pike :D On Tue, Sep 22, 2020 at 12:13 PM Rob Pike <r...@golang.org> wrote:
> I'm not going to debug you program for you - you'll learn more doing it > yourself, but I glanced at it and saw immediately that you're missing an > easy optimization. Raising a number to an integer power can be done much > faster by repeated squaring according to the bit pattern of the exponent. > I'll leave that cryptic comment alone to let you puzzle it out yourself. > (Don't look it up; it's much more fun to figure out.) > > -rob > > > On Tue, Sep 22, 2020 at 3:11 AM Hau Phan <haupc....@gmail.com> wrote: > >> i can't find get n-th root in document of go big package so i decided to >> do it myself using newton's method. i found a solution at >> https://www.geeksforgeeks.org/n-th-root-number/ and start to implement >> in go. but my code only work fine for base 2. other base result gone too >> far from correct. >> >> Anyone could show me where am i wrong. >> >> Here's my code >> >> ```go >> package main >> >> import ( >> "fmt" >> "math/big" >> "math/rand" >> ) >> >> // PowFloat return x^n >> func PowFloat(x *big.Float, n int64) *big.Float { >> result := new(big.Float).SetInt64(1) >> for i := 0; i < int(n); i++ { >> result.Mul(result, x) >> } >> return result >> } >> >> // GetNthRoothFloat get nth root of a using newton's method >> func GetNthRoothFloat(a *big.Float, n int64) *big.Float { >> N := new(big.Float).SetInt64(n) >> xPre := new(big.Float).SetInt64(int64(rand.Intn(10) + 1)) >> eps := new(big.Float).SetFloat64(0.00000000001) >> delX := new(big.Float).SetInt64(2147483647) >> xK := new(big.Float).SetInt64(0) >> >> for delX.Cmp(eps) > 0 { >> t1 := new(big.Float).Sub(N, new(big.Float).SetFloat64(1.0)) // t1 = n-1 >> t1 = t1.Mul(t1, xPre) // t1 = (N-1) >> * xPre >> t2 := new(big.Float).Quo(a, PowFloat(xPre, n-1)) // t2 = a/( >> xPre^(n-1) ) >> t3 := new(big.Float).Add(t1, t2) // t3 = t1 + >> t2 >> xK.Quo(t3, N) >> delX = new(big.Float).Sub(xK, xPre) >> delX.Abs(delX) >> xPre = xK.Copy(xK) >> } >> return xK >> } >> >> func main() { >> t := new(big.Float).SetInt64(64) >> fmt.Println(GetNthRoothFloat(t, 3)) >> } >> ``` >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/5a38a7fe-426b-4f94-905e-79b42dcaa611n%40googlegroups.com >> <https://groups.google.com/d/msgid/golang-nuts/5a38a7fe-426b-4f94-905e-79b42dcaa611n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/CAOXNBZQrjBjT-dDEK1Atu7R32aT1mgTsSAYhXAF7hXmj35BjuQ%40mail.gmail.com > <https://groups.google.com/d/msgid/golang-nuts/CAOXNBZQrjBjT-dDEK1Atu7R32aT1mgTsSAYhXAF7hXmj35BjuQ%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAG9C_MeG0P%3DSy5732WvW-EfsreSObQve%3DLsEUms%3DdWdRenvZ4Q%40mail.gmail.com.
