fpcMotif · October 27, 2018 06:40 · Apr 24, 2012
diff --git a/lagrange.py b/lagrange.py
@@ -0,0 +1,64 @@
+
+import numpy as np
+import matplotlib.pyplot as plt
+import sys
+
+def main():
+	if len(sys.argv) == 1 or "-h" in sys.argv or "--help" in sys.argv:
+		print "python lagrange.py <x1.y1> .. <x_k.y_k>"
+		print "Example:"
+		print "python lagrange.py 0.1 2.4 4.5 3.2"
+		exit()
+	points = []
+	for i in xrange(len(sys.argv)): 
+		if i != 0: 
+			points.append((int(sys.argv[i].split(".")[0]),int(sys.argv[i].split(".")[1]))) 
+
+	#points =[(0,0),(25,30),(50,10), (57,0)]
+	P = lagrange(points)
+	nr = 2
+	print "(" + str(points[nr][0]) + ", " + str(points[nr][1]) +") P(" + str(points[nr][0]) +")= " +str(P(points[nr][0]))
+	plot(P, points)
+
+def plot(f, points):
+	x = range(-10, 100)
+	y = map(f, x)
+	print y
+	plt.plot( x, y, linewidth=2.0)
+	x_list = []
+	y_list = []
+	for x_p, y_p in points:
+		x_list.append(x_p)
+		y_list.append(y_p)
+	print x_list
+	print y_list
+	plt.plot(x_list, y_list,  'ro')
+
+	plt.show()
+
+
+def lagrange(points):
+	def P(x):
+		total = 0
+		n = len(points)
+		for i in xrange(n):
+			xi, yi = points[i]
+
+			def g(i, n):
+
+				tot_mul = 1
+				for j in xrange(n):
+					if i == j:
+						continue
+					xj, yj = points[j]
+					tot_mul *= (x - xj) / float(xi - xj)
+
+				return tot_mul 
+
+			total += yi * g(i, n)
+		return total
+	return P 
+
+
+if __name__ == "__main__":
+	main()
No results found