# -*- coding: utf-8 -*-
"""
Created on Thu Sep  2 15:55:14 2021

@author: Rene
"""

import pandas as pd
import numpy as np
from scipy.stats import t
from scipy.stats import norm

def get_conf_int_var_known(x,alpha,sigma):
    n = len(x)
    x_bar = np.mean(x)
    st_dev_x_bar = sigma/(n**0.5)
    half_width = norm.ppf(1-(alpha/2),0,1)*st_dev_x_bar
    bounds = np.zeros(2)
    bounds[0] = x_bar-half_width
    bounds[1] = x_bar+half_width
    return(bounds)

def get_conf_int_var_unknown(x,alpha):
    n = len(x)
    x_bar = np.mean(x)
    st_dev_x_bar = np.std(x,ddof=1)/(n**0.5)
    half_width = t.ppf(1-(alpha/2),n-1)*st_dev_x_bar
    bounds = np.zeros(2)
    bounds[0] = x_bar-half_width
    bounds[1] = x_bar+half_width
    return(bounds)

df = pd.read_csv('coal.csv')
CalContent = df["Calorific Content"]
alpha=0.05
the_sigma = 0.1
conf_bounds_known = get_conf_int_var_known(CalContent,alpha,the_sigma)
print(conf_bounds_known)
conf_bounds_unknown = get_conf_int_var_unknown(CalContent,alpha)
print(conf_bounds_unknown)