import numpy
import pylab
from numpy.polynomial import polyfit

data = numpy.loadtxt('data_fitting.dat')
t = data[:,0]
v = data[:,1]
s = data[:,2]

poly = numpy.polyfit(t,v,3)

gA = numpy.arange(-1,1,0.1)
gB = numpy.arange(0,2,0.1)
gC = numpy.arange(1,2,0.1)
gD = numpy.arange(-1,1,0.1)

minchi = 1e20

for w in range(0,gA.size):
    for x in range(0,gB.size):
        for y in range(0,gC.size):
            for z in range(0,gD.size):
                f = gA[w] + t*gB[x] + t*gC[y]**2 + t*gD[z]**3
                chi = numpy.sum((v-f)**2/s**2)
                if chi < minchi:
                    bA = gA[w]
                    bB = gB[x]
                    bC = gC[y]
                    bD = gD[z]
                    minchi = chi

f = bA + t*bB + t*bC**2 + t*bD**3

pylab.figure(1)
pylab.plot(t,f)
pylab.errorbar(t,v,yerr=s,ls='none')
pylab.show()