From f5d1a13a18d9a2c179d88b921cebec0f2a9e8cfe Mon Sep 17 00:00:00 2001
From: Jiri Pittner <jiri@pittnerovi.com>
Date: Tue, 9 Nov 2021 13:19:24 +0100
Subject: [PATCH] NRPerm::reverse

---
 permutation.cc | 12 ++++++++++++
 permutation.h  |  1 +
 2 files changed, 13 insertions(+)

diff --git a/permutation.cc b/permutation.cc
index ee5cf7f..4b0c4a7 100644
--- a/permutation.cc
+++ b/permutation.cc
@@ -79,6 +79,18 @@ for(T i=1; i<=this->size(); ++i) q[(*this)[i]]=i;
 return q;
 }
 
+template <typename T>
+NRPerm<T> NRPerm<T>::reverse() const
+{
+#ifdef DEBUG
+        if(!this->is_valid()) laerror("reverse of invalid permutation");
+#endif
+
+NRPerm<T> q(this->size());
+for(T i=1; i<=this->size(); ++i) q[i]=(*this)[this->size()-i+1];
+return q;
+}
+
 
 template <typename T>
 NRPerm<T> NRPerm<T>::operator*(const NRPerm<T> q) const
diff --git a/permutation.h b/permutation.h
index 1ab744a..fb69c5a 100644
--- a/permutation.h
+++ b/permutation.h
@@ -52,6 +52,7 @@ public:
 	bool is_valid() const; //is it really a permutation
 	bool is_identity() const;
 	NRPerm inverse() const;
+	NRPerm reverse() const; //backward order
 	NRPerm operator*(const NRPerm q) const; //q is rhs and applied first, this applied second
 	NRPerm conjugate_by(const NRPerm q) const; //q^-1 p q
 	int parity() const;