From e0c570107becceb0e354861c9978b1c8350b4931 Mon Sep 17 00:00:00 2001
From: NunoSempere <nuno.semperelh@protonmail.com>
Date: Fri, 10 May 2024 19:25:23 +0100
Subject: [PATCH] reach initial mvp

---
 main.go | 56 +++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 41 insertions(+), 15 deletions(-)

diff --git a/main.go b/main.go
index 34d31da..a841d2d 100644
--- a/main.go
+++ b/main.go
@@ -3,22 +3,49 @@ package main
 import (
 	"bufio"
 	"fmt"
+	"math"
 	"os"
 	"strconv"
 	"strings"
 )
 
-// combineFloats takes previous stored floats and new floats, applies an operation, and returns the combined results.
-func combineFloats(stored1, stored2, new1, new2 float64) (float64, float64) {
-	// Example operation: simply adding the new floats to the stored ones.
-	return stored1 + new1, stored2 + new2
+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 stored1, stored2 float64 // Variables to store the intermediate results
+	var old_low, old_high float64 // Variables to store the intermediate results
 
-	fmt.Println("Enter two floats separated by a space:")
+	// fmt.Println("Enter two floats separated by a space:")
 	input, _ := reader.ReadString('\n')
 	input = strings.TrimSpace(input)
 
@@ -27,17 +54,17 @@ func main() {
 		fmt.Println("Please enter exactly two floats.")
 		return
 	}
-	stored1, err1 := strconv.ParseFloat(tokens[0], 64)
-	stored2, err2 := strconv.ParseFloat(tokens[1], 64)
+	old_low, err1 := strconv.ParseFloat(tokens[0], 64)
+	old_high, err2 := strconv.ParseFloat(tokens[1], 64)
 	if err1 != nil || err2 != nil {
 		fmt.Println("Invalid input. Please ensure you enter two floats.")
 		return
 	}
 
-	fmt.Printf("=> %.1f %.1f\n", stored1, stored2)
+	fmt.Printf("=> %.1f %.1f\n", old_low, old_high)
 
 	for {
-		fmt.Println("Enter another two floats separated by a space:")
+		// fmt.Println("Enter another two floats separated by a space:")
 		input, _ = reader.ReadString('\n')
 		if strings.TrimSpace(input) == "" {
 			break // Exit if no input is given
@@ -49,16 +76,15 @@ func main() {
 			continue
 		}
 
-		new1, err1 := strconv.ParseFloat(tokens[0], 64)
-		new2, err2 := strconv.ParseFloat(tokens[1], 64)
+		new_low, err1 := strconv.ParseFloat(tokens[0], 64)
+		new_high, err2 := strconv.ParseFloat(tokens[1], 64)
 		if err1 != nil || err2 != nil {
 			fmt.Println("Invalid input. Please ensure you enter two floats.")
 			continue
 		}
 
 		// Use the abstracted function for combining floats
-		stored1, stored2 = combineFloats(stored1, stored2, new1, new2)
-
-		fmt.Printf("=> %.1f %.1f\n", stored1, stored2)
+		old_low, old_high = combineBounds(old_low, old_high, new_low, new_high)
+		fmt.Printf("=> %.1f %.1f\n", old_low, old_high)
 	}
 }