From e09171467b329da71f934dc1a476f1bf78051f43 Mon Sep 17 00:00:00 2001
From: Jiri Pittner <jiri@pittnerovi.com>
Date: Mon, 8 Apr 2024 16:02:46 +0200
Subject: [PATCH] inverse_simplicial fix

---
 miscfunc.cc |  6 ++++--
 t.cc        | 13 +++++++++----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/miscfunc.cc b/miscfunc.cc
index cf50929..1c21ac4 100644
--- a/miscfunc.cc
+++ b/miscfunc.cc
@@ -811,7 +811,7 @@ return stored[d-2][n];
 }
 
 
-
+//find largest n such that simplicial(d,n)<=s
 int inverse_simplicial(int d,  unsigned long long s)
 {
 if(s==0) return 0;
@@ -841,7 +841,9 @@ do
 	x -= dx;
 	}
 while(std::fabs(dx)>.5); //so usually 2 iterations are enough
-return std::floor(x);
+int n=  std::floor(x);
+while(simplicial(d,n)>s) --n;
+return n;
 }
 
 #undef SIMPLICIAL_MAXD
diff --git a/t.cc b/t.cc
index e279a2a..bcdf2ef 100644
--- a/t.cc
+++ b/t.cc
@@ -3180,10 +3180,15 @@ if(1)
 {
 int d,n;
 cin>>d>>n;
-unsigned long long s;
-s=simplicial(d,n);
-cout <<s<<" "<<binom(n+d-1,d)<<endl;
-cout <<inverse_simplicial(d,s)<<endl;
+unsigned long long s1;
+s1=simplicial(d,n);
+cout <<s1<<" "<<binom(n+d-1,d)<<endl;
+unsigned long long s2 = simplicial(d,n+1);
+for(unsigned long long  s=s1; s<s2; ++s) 
+	{
+	int i=inverse_simplicial(d,s);
+	if(i!=n) cout <<"Error "<<s<<" " <<i<<endl;
+	}
 }
 
 if(0)