A small script to interpolate data points and return a polynomial going through those points.

gistfile1.txt

'''
README

To use this script you must have python and numpy installed.
Just download the script, open up the terminal and execute the
 script as './interpolate.py -i' for the interactive mode 
and './interpolate -f file' to use a file as the data source.
 the file must be formatted as input/output pairs separated by a comma.

The script will print a list as output. The first number is the constant,
 the second is the coefficient of x, the third of x^2 and so on.

For any more info, contact Sayantan Khan at bolt.khan@gmail.com
'''

import numpy as np

class InvalidDataError(Exception):
	pass

def interpolator(data_points): 
	poly_degree=len(data_points)-1
	number_of_variables=len(data_points)
	main_array=np.array([[i[0]**j for j in range(0,poly_degree+1)]+[i[1]] for i in data_points])
	primary_array=main_array[:,:-1]
	primary_array_det=np.linalg.det(primary_array)

	if primary_array_det!=0:
		variables=[]
		for i in range(number_of_variables):
			temp_det=np.linalg.det(np.delete(main_array,i,1))*(-1)**(number_of_variables-(i+1))
			varial=temp_det/primary_array_det
			variables.append(varial)
		return variables	
	else:
		raise InvalidDataError()

def file_parser(file_object):
	content=file_object.readlines()
	return_list=[[float(j) for j in i.strip().split(',')] for i in content]	
	return return_list
def diff_poly(coeff_list,number_of_times=1):
	print('i')
	if number_of_times!=0:
		if coeff_list!=[0]:
			for i in range(len(coeff_list)):
				coeff_list[i]=coeff_list[i]*i
			coeff_list.pop(0)
		elif coeff_list==[0]:
			pass
		return diff_poly(coeff_list,number_of_times-1)	
	elif number_of_times==0:
		return coeff_list

if __name__=='__main__':
	from sys import argv
	if argv[1]=='-i':
		input_val=[]
		print("Enter the input/output pair as comma separated values.")
		while True:
			inputs=raw_input()
			if inputs!='':
				input_val.append([int(i) for i in inputs.split(',')])
			elif inputs=='':
				break
		print(interpolator(input_val))
	elif argv[1]=='-f':
		file_obj=open(argv[2])
		print(interpolator(file_parser(file_obj)))