59 lines
1.0 KiB
Go
59 lines
1.0 KiB
Go
package main
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import (
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"fmt"
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"math"
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"os"
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"strconv"
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)
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const usage = "usage: sqrt <number>"
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const min_threshold = 1e-16
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type ErrNegativeSqrt float64
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func (e ErrNegativeSqrt) Error() string {
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return fmt.Sprintf("cannot Sqrt negative number: %v", float64(e))
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}
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func Sqrt(x float64, threshold float64) (z float64, iterations int, err error) {
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if x < 0 {
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err = ErrNegativeSqrt(x)
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return
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}
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z = x
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old_z := z
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for {
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z = z - (z*z-x)/(2*x)
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if math.Abs(z-old_z) < threshold {
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break
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}
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old_z = z
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iterations++
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}
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return
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}
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func main() {
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if len(os.Args) != 2 {
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fmt.Fprintf(os.Stderr, "%v\n", usage)
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os.Exit(1)
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}
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i, err := strconv.ParseFloat(os.Args[1], 32)
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if err != nil {
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panic(err)
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}
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threshold := 1.0
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right_answer := math.Sqrt(i)
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for threshold > min_threshold {
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answer, iterations, err := Sqrt(i, threshold)
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if err != nil {
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panic(err)
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}
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fmt.Printf("%0.4E %0.4d %0.20f %0.20f %0.4e\n",
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threshold, iterations, right_answer, answer,
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right_answer-answer)
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threshold = threshold / 10.0
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}
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}
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