#!/usr/bin/env python3
#
# day2-ex1.py - parabola data visualisation

import ROOT

Vtrue = [0, 1, 2, 3, 4, 5]
V = [-.10, .84, 1.91, 2.88, 4.06, 4.83]
sigmas = [.1, .1, .1, .1, .1, .1]

ROOT.gROOT.SetBatch()
c = ROOT.TCanvas("c", "c", 800, 600)

# build graph with data
gdata = ROOT.TGraphErrors(len(Vtrue))
gdata.SetNameTitle("gdata", "data")
for i in range(0, len(Vtrue)):
    gdata.SetPoint(i, Vtrue[i], V[i])
    gdata.SetPointError(i, 0., sigmas[i])
gdata.SetLineWidth(2)
gdata.SetMarkerStyle(7)
gdata.SetMarkerSize(2)

gdata.Draw("AP")  # draw data

l = ROOT.TLegend(0.2, 0.7, 0.4, 0.9)
l.AddEntry(gdata)
l.Draw()

c.SaveAs("day2-ex1.pdf")
c.SaveAs("day2-ex1.png")