fermi/f.go

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

const NORMAL90CONFIDENCE = 1.6448536269514727

func boundsToLogParams(low float64, high float64) (float64, float64) {
	loglow := math.Log(low)
	loghigh := math.Log(high)
	logmean := (loghigh + loglow) / 2.0
	logstd := (loghigh - loglow) / (2.0 * NORMAL90CONFIDENCE)
	return logmean, logstd

}

func multiplyLognormals(logmean1 float64, logstd1 float64, logmean2 float64, logstd2 float64) (float64, float64) {
	return logmean1 + logmean2, math.Sqrt(logstd1*logstd1 + logstd2*logstd2)
}

func logParamsToBounds(logmean float64, logstd float64) (float64, float64) {
	h := logstd * NORMAL90CONFIDENCE
	loglow := logmean - h
	loghigh := logmean + h
	return math.Exp(loglow), math.Exp(loghigh)
}

func combineBounds(old_low, old_high, new_low, new_high float64) (float64, float64) {
	logmean_old, logstd_old := boundsToLogParams(old_low, old_high)
	logmean_new, logstd_new := boundsToLogParams(new_low, new_high)

	logmean_product, logstd_product := multiplyLognormals(logmean_old, logstd_old, logmean_new, logstd_new)

	return logParamsToBounds(logmean_product, logstd_product)
}

func main() {
	reader := bufio.NewReader(os.Stdin)

	var old_low, old_high float64
	var input string
	var err1, err2 error
	for {
		input, _ = reader.ReadString('\n')
		input = strings.TrimSpace(input)
		words := strings.Split(input, " ")
		if len(words) != 2 {
			fmt.Println("Please enter two floats separated by a space, like: 1 10")
			continue
		}
		old_low, err1 = strconv.ParseFloat(words[0], 64)
		old_high, err2 = strconv.ParseFloat(words[1], 64)
		if err1 != nil || err2 != nil {
			fmt.Println("Please enter two floats separated by a space, like: 1 10")
			continue
		}
		break

	}
	fmt.Printf("=> %.1f %.1f\n", old_low, old_high)

	error_msg_cont := "Valid inputs: 2 || * 2 || / 2 || 2 20 || * 2 20 || / 2 20 || i || e"
EventForLoop:
	for {
		input, _ = reader.ReadString('\n')
		if strings.TrimSpace(input) == "" {
			continue EventForLoop
		}
		words := strings.Split(strings.TrimSpace(input), " ")

		var new_low, new_high float64

		switch words[0] {
		case "*":
			switch len(words) {
			case 1:
				fmt.Println("Can't multiply by nothing")
				fmt.Println(error_msg_cont)
				continue EventForLoop
			case 2:
				single_float, err1 := strconv.ParseFloat(words[1], 64)
				if err1 != nil {
					fmt.Println("Trying to multiply by a scalar, but scalar is not a float")
					fmt.Println(error_msg_cont)
					continue EventForLoop
				}
				new_low = single_float
				new_high = single_float
			case 3:
				new_low, err1 = strconv.ParseFloat(words[1], 64)
				new_high, err2 = strconv.ParseFloat(words[2], 64)
				if err1 != nil || err2 != nil {
					fmt.Println(error_msg_cont)
					fmt.Println("Trying to multiply by a distribution, but distribution is not specified as two floats")
					continue EventForLoop
				}
			default:
				fmt.Println("Trying to multiply by something, but this something is neither a scalar nor a distribution")
				fmt.Println(error_msg_cont)
				continue EventForLoop
			}
		case "/":
			switch len(words) {
			case 1:
				fmt.Println("Can't divide by nothing")
				fmt.Println(error_msg_cont)
				continue EventForLoop
			case 2:
				single_float, err1 := strconv.ParseFloat(words[1], 64)
				if err1 != nil {
					fmt.Println("Trying to divide by a scalar, but scalar is not a float")
					fmt.Println(error_msg_cont)
					continue EventForLoop
				}
				new_low = 1.0 / single_float
				new_high = 1.0 / single_float
			case 3:
				new_low, err1 = strconv.ParseFloat(words[1], 64)
				new_high, err2 = strconv.ParseFloat(words[2], 64)
				if err1 != nil || err2 != nil {
					fmt.Println("Trying to divide by a distribution, but distribution is not specified as two floats")
					fmt.Println(error_msg_cont)
					continue EventForLoop
				}
			default:
				fmt.Println("Trying to divide by something, but this something is neither a scalar nor a distribution")
			}
		default:
			switch len(words) {
			case 0:
				continue EventForLoop
			case 1:
				switch words[0] {
				case "i":
					fmt.Printf("=> %.1f %.1f\n", old_low, old_high)
					logmean_old, logstd_old := boundsToLogParams(old_low, old_high)
					fmt.Printf("=> Lognormal, with logmean: %.1f, logstd: %.1f\n", logmean_old, logstd_old)
					continue EventForLoop
				case "e":
					break EventForLoop
				default:
					single_float, err1 := strconv.ParseFloat(words[0], 64)
					if err1 != nil {
						fmt.Println("Unrecognized command")
						fmt.Println(error_msg_cont)
						continue EventForLoop
					}
					new_low = single_float
					new_high = single_float
				}
			case 2:
				new_low, err1 = strconv.ParseFloat(words[0], 64)
				new_high, err2 = strconv.ParseFloat(words[1], 64)
				if err1 != nil || err2 != nil {
					fmt.Println("Trying to multiply by a distribution, but distribution is not specified as two floats")
					fmt.Println(error_msg_cont)
					continue EventForLoop
				}
			default:
				fmt.Println("No operation takes more than 3 words")
				fmt.Println(error_msg_cont)
				continue EventForLoop
			}
		}

		old_low, old_high = combineBounds(old_low, old_high, new_low, new_high)
		fmt.Printf("=> %.1f %.1f\n", old_low, old_high)
	}
}