From 629e1bc3ae1fbafd5c999617535efb4aec816240 Mon Sep 17 00:00:00 2001
From: "dario.genga" <dario.genga@etu.hesge.ch>
Date: Wed, 8 Dec 2021 16:06:17 +0100
Subject: [PATCH] Add lagrange polynomial
The prime number is not used for now.
---
polynomial.py | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/polynomial.py b/polynomial.py
index 6268848..09d8263 100644
--- a/polynomial.py
+++ b/polynomial.py
@@ -1,3 +1,4 @@
+import math
from numbers import Number
import itertools
import json
@@ -77,6 +78,7 @@ class Polynomial:
str_value = ""
for i, x in enumerate(reversed(self.value)):
+ x = math.ceil(x)
if x == 0:
continue
if i != 0:
@@ -135,7 +137,29 @@ def modular_inverse(a, n):
def compute_lagrange_polynomial(points, prime_number):
- pass
+ nb_points = len(points)
+ lagrange = Polynomial((0,))
+
+ # Create a polynomial for each points
+ for i in range(nb_points):
+ poly_li = Polynomial((1,))
+ divider = 1
+
+ # Compute the lagrange polynomial
+ for k in range(nb_points):
+ if k != i:
+ dividend = Polynomial((-points[k][0], 1)) # x - value
+
+ poly_li *= dividend
+ divider *= (points[i][0] - points[k][0])
+
+ divider = 1 / divider
+ point_yi = points[i][1]
+ poly_li = poly_li * Polynomial((divider,)) * Polynomial((point_yi,))
+
+ lagrange += poly_li
+
+ return lagrange
def reed_solomon(points, data_length, last_error_index, prime_number):
--
GitLab