From 1bd4267773a6368eef86d75242eeb3a2834356fa Mon Sep 17 00:00:00 2001
From: mantikoros <sgrugett@gmail.com>
Date: Thu, 28 Apr 2022 10:30:44 -0400
Subject: [PATCH] contrain liquidity paramter p to [0.1, 0.9]

---
 common/new-contract.ts | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/common/new-contract.ts b/common/new-contract.ts
index ffd27e3f..79319d01 100644
--- a/common/new-contract.ts
+++ b/common/new-contract.ts
@@ -87,15 +87,22 @@ const getBinaryDpmProps = (initialProb: number, ante: number) => {
   return system
 }
 
-const getBinaryCpmmProps = (initialProb: number, ante: number) => {
-  const pool = { YES: ante, NO: ante }
-  const p = initialProb / 100
+const getBinaryCpmmProps = (initialProbInt: number, ante: number) => {
+  const prob = initialProbInt / 100
+
+  // constrain parameter to [0.1, 0.9]
+  const p = prob > 0.9 ? 0.9 : prob < 0.1 ? 0.1 : prob
+
+  const pool = {
+    YES: prob > 0.9 ? (ante * p * (prob - 1)) / ((p - 1) * prob) : ante,
+    NO: prob < 0.1 ? (ante * (p - 1) * prob) / (p * (prob - 1)) : ante,
+  }
 
   const system: CPMM & Binary = {
     mechanism: 'cpmm-1',
     outcomeType: 'BINARY',
     totalLiquidity: ante,
-    initialProbability: p,
+    initialProbability: prob,
     p,
     pool: pool,
   }