From 1677d6337505994869c196229c5edd2788a1353e Mon Sep 17 00:00:00 2001
From: NunoSempere <nuno.sempere@protonmail.com>
Date: Thu, 14 Apr 2022 21:53:45 -0400
Subject: [PATCH] fix: std of lognormal symbolic division

---
 .../src/rescript/Distributions/SymbolicDist/SymbolicDist.res    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
index afd35800..0ef8b3d0 100644
--- a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
@@ -167,7 +167,7 @@ module Lognormal = {
     let mu = l1.mu -. l2.mu
     // We believe the ratiands will have covariance zero.
     // See here https://stats.stackexchange.com/questions/21735/what-are-the-mean-and-variance-of-the-ratio-of-two-lognormal-variables for details
-    let sigma = l1.sigma +. l2.sigma
+    let sigma = Js.Math.sqrt(l1.sigma ** 2. +. l2.sigma ** 2.) // m
     #Lognormal({mu: mu, sigma: sigma})
   }
   let operate = (operation: Operation.Algebraic.t, n1: t, n2: t) =>