From 06d1065bb91fc2b2ddc20195b58a9e8051a67a6c Mon Sep 17 00:00:00 2001
From: David Florness <david@florness.com>
Date: Mon, 8 Jun 2020 22:51:10 -0600
Subject: [PATCH] Find the constant term of the result polynomial

---
 linalg.go | 26 ++++++++++++++++----------
 voter.go  | 43 ++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 56 insertions(+), 13 deletions(-)

diff --git a/linalg.go b/linalg.go
index 6b75606..42c7355 100644
--- a/linalg.go
+++ b/linalg.go
@@ -6,26 +6,32 @@ import (
 
 type Matrix [][]big.Rat
 
+func (M Matrix) Rows() int {
+	return len(M)
+}
+
+func (M Matrix) Cols() int {
+	if len(M) == 0 {
+		return 0
+	}
+	return len(M[0])
+}
+
 func (M Matrix) RREF() {
 	lead := 0
-	rowCount := len(M)
-	if rowCount == 0 {
-		return
-	}
-	columnCount := len(M[0])
 	zero := big.NewRat(0, 1)
 
-	for r := 0; r < rowCount; r++ {
-		if lead >= columnCount {
+	for r := 0; r < M.Rows(); r++ {
+		if lead >= M.Cols() {
 			return
 		}
 		i := r
 		for M[i][lead].Cmp(zero) == 0 {
 			i++
-			if rowCount == i {
+			if M.Rows() == i {
 				i = r
 				lead++
-				if columnCount == lead {
+				if M.Cols() == lead {
 					return
 				}
 			}
@@ -36,7 +42,7 @@ func (M Matrix) RREF() {
 		for j := range M[r] {
 			M[r][j].Mul(&M[r][j], f)
 		}
-		for i = 0; i < rowCount; i++ {
+		for i = 0; i < M.Rows(); i++ {
 			if i != r {
 				f.Set(&M[i][lead])
 				for j, e := range M[r] {
diff --git a/voter.go b/voter.go
index 6d3d266..67169a6 100644
--- a/voter.go
+++ b/voter.go
@@ -188,7 +188,7 @@ func findPeers(closeElection <-chan int) {
 	discovery.Advertise(me.ctx, routingDiscovery, string(rendezvousNonce))
 	logger.Info("successfully announced!")
 
-	logger.Info("searching for other voters...")
+	fmt.Println("finding other voters...")
 	peerChan, err := routingDiscovery.FindPeers(me.ctx, string(rendezvousNonce))
 	if err != nil {
 		panic(err)
@@ -203,7 +203,7 @@ func findPeers(closeElection <-chan int) {
 			if peer.ID == me.ID() {
 				continue
 			}
-			logger.Info("found voter:", peer)
+			fmt.Printf("found voter: %s\n", peer)
 			logger.Info("connecting to:", peer)
 
 			err = me.Connect(me.ctx, peer)
@@ -230,7 +230,7 @@ func findPeers(closeElection <-chan int) {
 
 func (voter *Voter) fetchNumber(cmd string, args ...string) *big.Int {
 	printErr := func(err error, msg string) {
-		logger.Errorf("%s: %s fetcing `%s'; retrying in 2 seconds",
+		logger.Errorf("%s: %s while fetcing `%s'; retrying in 2 seconds",
 			voter.addrInfo.ID, msg, cmd)
 		time.Sleep(time.Second * 2)
 	}
@@ -289,11 +289,13 @@ func startVoting() {
 	logger.Infof("our input: %s", me.input)
 
 	ballot := vote(candidates)
+	logger.Info("our ballot:", ballot)
 
 	// no +1 since we want degree k-1 where k is total number of voters
 	me.polyMu.Lock()
 	me.poly = NewRandomPoly(uint(len(election.remoteVoters)), 1024, ballot)
 	me.polyMu.Unlock()
+	logger.Infof("our constant: %s", me.poly.constant)
 
 	// get outputs
 	var wg sync.WaitGroup
@@ -314,6 +316,7 @@ func startVoting() {
 		me.sum.Add(me.sum, voter.output)
 	}
 	me.sumMu.Unlock()
+	logger.Infof("our sum: %s", me.sum)
 
 	// get sums
 	for _, voter := range election.remoteVoters {
@@ -327,6 +330,40 @@ func startVoting() {
 	}
 	wg.Wait()
 
+	mat := constructPolyMatrix()
+	mat.RREF()
+
+	result := mat[0][len(mat[0])-1]
+
 	// temporary
 	select {}
 }
+
+func constructPolyMatrix() Matrix {
+	mat := make(Matrix, len(election.remoteVoters) + 1) // row for everyone (including ourselves)
+
+	i := 0
+	for _, voter := range election.remoteVoters {
+		mat[i] = make([]big.Rat, len(mat) + 1) // includes column for sum
+		row := mat[i]
+		row[0].SetInt64(1)
+		var j int64
+		for j = 1; j <= int64(len(election.remoteVoters)); j++ {
+			row[j].SetInt(new(big.Int).Exp(voter.input, big.NewInt(j), nil))
+		}
+		row[j].SetInt(voter.sum)
+		i++
+	}
+
+	// row for ourselves
+	mat[i] = make([]big.Rat, len(mat) + 1)
+	row := mat[i]
+	row[0].SetInt64(1)
+	var j int64
+	for j = 1; j <= int64(len(election.remoteVoters)); j++ {
+		row[j].SetInt(new(big.Int).Exp(me.input, big.NewInt(j), nil))
+	}
+	row[j].SetInt(me.sum)
+
+	return mat
+}
-- 
2.38.4