From 5bb015ab692f3b408ca19fb20799bd5de38a60a1 Mon Sep 17 00:00:00 2001
From: NunoSempere <nuno.semperelh@protonmail.com>
Date: Sun, 9 Jun 2024 14:00:30 +0200
Subject: [PATCH] simplify lognormal multiplication code

---
 f2.go | 44 +++++++++++++++++++-------------------------
 1 file changed, 19 insertions(+), 25 deletions(-)

diff --git a/f2.go b/f2.go
index 3dbe89b..7c8f53f 100644
--- a/f2.go
+++ b/f2.go
@@ -26,6 +26,9 @@ type Dist struct {
 
 // Parse line into Distribution
 func parseLineErr(err_msg string) (string, Dist, error) {
+	general_err_msg := "Valid inputs: 2 || * 2 || / 2 || 2 20 || * 2 20 || / 2 20 || i || e"
+	fmt.Println(general_err_msg)
+	fmt.Println(err_msg)
 	return "", Dist{}, errors.New(err_msg)
 }
 func parseLine(line string) (string, Dist, error) {
@@ -51,11 +54,11 @@ func parseLine(line string) (string, Dist, error) {
 
 	switch len(words) {
 	case 0:
-		return parseLineErr("Can't operate on nothing")
+		return parseLineErr("Operator must have operand; can't operate on nothing")
 	case 1:
 		single_float, err1 := strconv.ParseFloat(words[0], 64)
 		if err1 != nil {
-			fmt.Println("Trying to operate on a scalar, but scalar is not a float")
+			return parseLineErr("Trying to operate on a scalar, but scalar is not a float")
 		}
 		dist = Dist{Type: "Lognormal", Lognormal: Lognormal{low: single_float, high: single_float}, Samples: nil}
 	case 2:
@@ -75,36 +78,27 @@ func parseLine(line string) (string, Dist, error) {
 // Join distributions
 // Multiply lognormals
 
-func logBoundsToLogParams(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 logParamsToLogBounds(logmean float64, logstd float64) (float64, float64) {
-	h := logstd * NORMAL90CONFIDENCE
-	loglow := logmean - h
-	loghigh := logmean + h
-	return math.Exp(loglow), math.Exp(loghigh)
-}
-func multiplyLogParams(logmean1 float64, logstd1 float64, logmean2 float64, logstd2 float64) (float64, float64) {
-	return logmean1 + logmean2, math.Sqrt(logstd1*logstd1 + logstd2*logstd2)
-}
-func multiplyLogBounds(old_low, old_high, new_low, new_high float64) (float64, float64) {
-	logmean_old, logstd_old := logBoundsToLogParams(old_low, old_high)
-	logmean_new, logstd_new := logBoundsToLogParams(new_low, new_high)
+func multiplyLogDists(l1 Lognormal, l2 Lognormal) Lognormal {
+	logmean1 := (math.Log(l1.high) + math.Log(l1.low)) / 2.0
+	logstd1 := (math.Log(l1.high) - math.Log(l1.low)) / (2.0 * NORMAL90CONFIDENCE)
 
-	logmean_product, logstd_product := multiplyLogParams(logmean_old, logstd_old, logmean_new, logstd_new)
+	logmean2 := (math.Log(l2.high) + math.Log(l2.low)) / 2.0
+	logstd2 := (math.Log(l2.high) - math.Log(l2.low)) / (2.0 * NORMAL90CONFIDENCE)
+
+	logmean_product := logmean1 + logmean2
+	logstd_product := math.Sqrt(logstd1*logstd1 + logstd2*logstd2)
+
+	h := logstd_product * NORMAL90CONFIDENCE
+	loglow := logmean_product - h
+	loghigh := logmean_product + h
+	return Lognormal{low: math.Exp(loglow), high: math.Exp(loghigh)}
 
-	return logParamsToLogBounds(logmean_product, logstd_product)
 }
 
 func joinDists(old_dist Dist, new_dist Dist, op string) (Dist, error) {
 	switch {
 	case old_dist.Type == "Lognormal" && new_dist.Type == "Lognormal" && op == "*":
-		low, high := multiplyLogBounds(old_dist.Lognormal.low, old_dist.Lognormal.high, new_dist.Lognormal.low, new_dist.Lognormal.high)
-		return Dist{Type: "Lognormal", Lognormal: Lognormal{low: low, high: high}, Samples: nil}, nil
+		return Dist{Type: "Lognormal", Lognormal: multiplyLogDists(old_dist.Lognormal, new_dist.Lognormal), Samples: nil}, nil
 	default:
 		fmt.Printf("For now, can't do anything besides multiplying lognormals\n")
 	}