From 84bdfa004f946fe0aa2246a2b54ab18e274c5a5b Mon Sep 17 00:00:00 2001
From: NunoSempere <nuno.semperelh@protonmail.com>
Date: Wed, 20 Nov 2024 11:54:31 +0000
Subject: [PATCH] add some guards for edge cases

scalar = 0 * logdist
scalar < 1 * logdist
logdist with parameters < 0
logdist with same parameters (should be scalar)
logdist with low > high
---
 fermi.go | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/fermi.go b/fermi.go
index 8a4e4fc..581b95e 100644
--- a/fermi.go
+++ b/fermi.go
@@ -254,6 +254,16 @@ func multiplyBetaDists(beta1 Beta, beta2 Beta) Beta {
 	return Beta{a: beta1.a + beta2.a, b: beta1.b + beta2.b}
 }
 
+func multiplyLogDistAndScalar(l Lognormal, s Scalar) (Dist, error) {
+	if s == 0.0 {
+		return Scalar(0.0), nil
+	} else if s < 0.0 {
+		return operateDistsAsSamples(s, l, "+")
+	} else {
+		return multiplyLogDists(l, Lognormal{low: float64(s), high: float64(s)}), nil
+	}
+}
+
 func multiplyDists(old_dist Dist, new_dist Dist) (Dist, error) {
 
 	switch o := old_dist.(type) {
@@ -263,17 +273,20 @@ func multiplyDists(old_dist Dist, new_dist Dist) (Dist, error) {
 			case Lognormal:
 				return multiplyLogDists(o, n), nil
 			case Scalar:
-				return multiplyLogDists(o, Lognormal{low: float64(n), high: float64(n)}), nil
+				return multiplyLogDistAndScalar(o, n)
 			}
 		}
 	case Scalar:
 		{
-			if o == 1 {
+			switch o {
+			case 1.0:
 				return new_dist, nil
+			case 0.0:
+				return Scalar(0.0), nil
 			}
 			switch n := new_dist.(type) {
 			case Lognormal:
-				return multiplyLogDists(Lognormal{low: float64(o), high: float64(o)}, n), nil
+				return multiplyLogDistAndScalar(n, o)
 			case Scalar:
 				return Scalar(float64(o) * float64(n)), nil
 			}
@@ -304,14 +317,14 @@ func divideDists(old_dist Dist, new_dist Dist) (Dist, error) {
 					fmt.Println("Error: Can't divide by 0.0")
 					return nil, errors.New("Error: division by zero scalar")
 				}
-				return multiplyLogDists(o, Lognormal{low: 1.0 / float64(n), high: 1.0 / float64(n)}), nil
+				return multiplyLogDistAndScalar(o, Scalar(1.0/n))
 			}
 		}
 	case Scalar:
 		{
 			switch n := new_dist.(type) {
 			case Lognormal:
-				return multiplyLogDists(Lognormal{low: float64(o), high: float64(o)}, Lognormal{low: 1.0 / n.high, high: 1.0 / n.low}), nil
+				return multiplyLogDistAndScalar(Lognormal{low: 1.0 / n.high, high: 1.0 / n.low}, o)
 			case Scalar:
 				if n == 0.0 {
 					fmt.Println("Error: Can't divide by 0.0")
@@ -374,8 +387,15 @@ func parseWordsIntoOpAndDist(words []string, vars map[string]Dist) (string, Dist
 	case 2:
 		new_low, err1 := pretty.ParseFloat(words[0])
 		new_high, err2 := pretty.ParseFloat(words[1])
-		if err1 != nil || err2 != nil {
+		switch {
+		case err1 != nil || err2 != nil:
 			return parseWordsErr("Trying to operate by a distribution, but distribution is not specified as two floats")
+		case new_low <= 0.0 || new_high <= 0.0:
+			return parseWordsErr("Trying to parse two floats as a lognormal, but the two floats must be greater than 0")
+		case new_low == new_high:
+			return parseWordsErr("Trying to parse two floats as a lognormal, but the two floats must be different. Try a single scalar instead?")
+		case new_low > new_high:
+			return parseWordsErr("Trying to parse two floats as a lognormal, but the first number is larger than the second number")
 		}
 		dist = Lognormal{low: new_low, high: new_high}
 	case 3: