import pandas as pd
import numpy as np
#Leo el archivo txt
file="pendulo.txt"
Misdatos = np.loadtxt(file, delimiter="\t",skiprows=4)
#Datos ordenados col1 : x, col 2: y1
x1 = Misdatos[:,0]
y1= Misdatos[:,1]
#y2=y1**2
#print (Misdatos)

def ajustecm2(x, y):
    '''
    Ajuste de cuadrados minimos de una cuadratica del tipo:
    
    y(x) = a x  + b
    
    Modo de uso:
    
    In [ ]: a, b, sigmaa, sigmab, r2 = ajustecm2(x, y)
    
    '''
    import numpy as np
    coefs, covmat =np.polyfit(x, y, 1, full=False, cov=True)
    a = coefs[0]
    b = coefs[1]
    sigmaa = covmat[0,0]
    sigmab = covmat[1,1]
    
    # r cuadrado 
    p = np.poly1d(coefs)
    # valores auxiliares yfit e ymed
    yfit = p(x)                      
    ymed = np.sum(y)/len(y)          
    ssreg = np.sum((yfit - ymed)**2)   
    sstot = np.sum((y - ymed)**2)
    r2 = (ssreg/sstot)
    return a, b, sigmaa, sigmab, r2

Result=ajustecm2(x1, y1)
print("T^2 = a L + b  ")

print ("a=",Result[0],",  b=",Result[1],",  sigmaa=",Result[2],",  sigmab=",Result[3],",  r^2=",Result[4])