# -*- coding: utf-8 -*-
"""Tests of GLSAR and diagnostics against Gretl

Created on Thu Feb 02 21:15:47 2012

Author: Josef Perktold
License: BSD-3

"""

import os

import numpy as np
from numpy.testing import (assert_almost_equal, assert_equal,
                           assert_approx_equal, assert_array_less)

from statsmodels.regression.linear_model import OLS, GLSAR
from statsmodels.tools.tools import add_constant
from statsmodels.datasets import macrodata

import statsmodels.stats.sandwich_covariance as sw
import statsmodels.stats.diagnostic as smsdia
#import statsmodels.sandbox.stats.diagnostic as smsdia
import statsmodels.stats.outliers_influence as oi


def compare_ftest(contrast_res, other, decimal=(5,4)):
    assert_almost_equal(contrast_res.fvalue, other[0], decimal=decimal[0])
    assert_almost_equal(contrast_res.pvalue, other[1], decimal=decimal[1])
    assert_equal(contrast_res.df_num, other[2])
    assert_equal(contrast_res.df_denom, other[3])
    assert_equal("f", other[4])

class TestGLSARGretl(object):

    def test_all(self):

        d = macrodata.load().data
        #import datasetswsm.greene as g
        #d = g.load('5-1')

        #growth rates
        gs_l_realinv = 400 * np.diff(np.log(d['realinv']))
        gs_l_realgdp = 400 * np.diff(np.log(d['realgdp']))

        #simple diff, not growthrate, I want heteroscedasticity later for testing
        endogd = np.diff(d['realinv'])
        exogd = add_constant(np.c_[np.diff(d['realgdp']), d['realint'][:-1]])

        endogg = gs_l_realinv
        exogg = add_constant(np.c_[gs_l_realgdp, d['realint'][:-1]])

        res_ols = OLS(endogg, exogg).fit()
        #print res_ols.params

        mod_g1 = GLSAR(endogg, exogg, rho=-0.108136)
        res_g1 = mod_g1.fit()
        #print res_g1.params

        mod_g2 = GLSAR(endogg, exogg, rho=-0.108136)   #-0.1335859) from R
        res_g2 = mod_g2.iterative_fit(maxiter=5)
        #print res_g2.params


        rho = -0.108136

        #                 coefficient   std. error   t-ratio    p-value 95% CONFIDENCE INTERVAL
        partable = np.array([
                        [-9.50990,  0.990456, -9.602, 3.65e-018, -11.4631, -7.55670], # ***
                        [ 4.37040,  0.208146, 21.00,  2.93e-052,  3.95993, 4.78086], # ***
                        [-0.579253, 0.268009, -2.161, 0.0319, -1.10777, -0.0507346]]) #    **

        #Statistics based on the rho-differenced data:

        result_gretl_g1 = dict(
        endog_mean = ("Mean dependent var",   3.113973),
        endog_std = ("S.D. dependent var",   18.67447),
        ssr = ("Sum squared resid",    22530.90),
        mse_resid_sqrt = ("S.E. of regression",   10.66735),
        rsquared = ("R-squared",            0.676973),
        rsquared_adj = ("Adjusted R-squared",   0.673710),
        fvalue = ("F(2, 198)",            221.0475),
        f_pvalue = ("P-value(F)",           3.56e-51),
        resid_acf1 = ("rho",                 -0.003481),
        dw = ("Durbin-Watson",        1.993858))


        #fstatistic, p-value, df1, df2
        reset_2_3 = [5.219019, 0.00619, 2, 197, "f"]
        reset_2 = [7.268492, 0.00762, 1, 198, "f"]
        reset_3 = [5.248951, 0.023, 1, 198, "f"]
        #LM-statistic, p-value, df
        arch_4 = [7.30776, 0.120491, 4, "chi2"]

        #multicollinearity
        vif = [1.002, 1.002]
        cond_1norm = 6862.0664
        determinant = 1.0296049e+009
        reciprocal_condition_number = 0.013819244

        #Chi-square(2): test-statistic, pvalue, df
        normality = [20.2792, 3.94837e-005, 2]

        #tests
        res = res_g1  #with rho from Gretl

        #basic

        assert_almost_equal(res.params, partable[:,0], 4)
        assert_almost_equal(res.bse, partable[:,1], 6)
        assert_almost_equal(res.tvalues, partable[:,2], 2)

        assert_almost_equal(res.ssr, result_gretl_g1['ssr'][1], decimal=2)
        #assert_almost_equal(res.llf, result_gretl_g1['llf'][1], decimal=7) #not in gretl
        #assert_almost_equal(res.rsquared, result_gretl_g1['rsquared'][1], decimal=7) #FAIL
        #assert_almost_equal(res.rsquared_adj, result_gretl_g1['rsquared_adj'][1], decimal=7) #FAIL
        assert_almost_equal(np.sqrt(res.mse_resid), result_gretl_g1['mse_resid_sqrt'][1], decimal=5)
        assert_almost_equal(res.fvalue, result_gretl_g1['fvalue'][1], decimal=4)
        assert_approx_equal(res.f_pvalue, result_gretl_g1['f_pvalue'][1], significant=2)
        #assert_almost_equal(res.durbin_watson, result_gretl_g1['dw'][1], decimal=7) #TODO

        #arch
        #sm_arch = smsdia.acorr_lm(res.wresid**2, maxlag=4, autolag=None)
        sm_arch = smsdia.het_arch(res.wresid, maxlag=4)
        assert_almost_equal(sm_arch[0], arch_4[0], decimal=4)
        assert_almost_equal(sm_arch[1], arch_4[1], decimal=6)

        #tests
        res = res_g2 #with estimated rho

        #estimated lag coefficient
        assert_almost_equal(res.model.rho, rho, decimal=3)

        #basic
        assert_almost_equal(res.params, partable[:,0], 4)
        assert_almost_equal(res.bse, partable[:,1], 3)
        assert_almost_equal(res.tvalues, partable[:,2], 2)

        assert_almost_equal(res.ssr, result_gretl_g1['ssr'][1], decimal=2)
        #assert_almost_equal(res.llf, result_gretl_g1['llf'][1], decimal=7) #not in gretl
        #assert_almost_equal(res.rsquared, result_gretl_g1['rsquared'][1], decimal=7) #FAIL
        #assert_almost_equal(res.rsquared_adj, result_gretl_g1['rsquared_adj'][1], decimal=7) #FAIL
        assert_almost_equal(np.sqrt(res.mse_resid), result_gretl_g1['mse_resid_sqrt'][1], decimal=5)
        assert_almost_equal(res.fvalue, result_gretl_g1['fvalue'][1], decimal=0)
        assert_almost_equal(res.f_pvalue, result_gretl_g1['f_pvalue'][1], decimal=6)
        #assert_almost_equal(res.durbin_watson, result_gretl_g1['dw'][1], decimal=7) #TODO



        c = oi.reset_ramsey(res, degree=2)
        compare_ftest(c, reset_2, decimal=(2,4))
        c = oi.reset_ramsey(res, degree=3)
        compare_ftest(c, reset_2_3, decimal=(2,4))

        #arch
        #sm_arch = smsdia.acorr_lm(res.wresid**2, maxlag=4, autolag=None)
        sm_arch = smsdia.het_arch(res.wresid, maxlag=4)
        assert_almost_equal(sm_arch[0], arch_4[0], decimal=1)
        assert_almost_equal(sm_arch[1], arch_4[1], decimal=2)



        '''
        Performing iterative calculation of rho...

                         ITER       RHO        ESS
                           1     -0.10734   22530.9
                           2     -0.10814   22530.9

        Model 4: Cochrane-Orcutt, using observations 1959:3-2009:3 (T = 201)
        Dependent variable: ds_l_realinv
        rho = -0.108136

                         coefficient   std. error   t-ratio    p-value
          -------------------------------------------------------------
          const           -9.50990      0.990456    -9.602    3.65e-018 ***
          ds_l_realgdp     4.37040      0.208146    21.00     2.93e-052 ***
          realint_1       -0.579253     0.268009    -2.161    0.0319    **

        Statistics based on the rho-differenced data:

        Mean dependent var   3.113973   S.D. dependent var   18.67447
        Sum squared resid    22530.90   S.E. of regression   10.66735
        R-squared            0.676973   Adjusted R-squared   0.673710
        F(2, 198)            221.0475   P-value(F)           3.56e-51
        rho                 -0.003481   Durbin-Watson        1.993858
        '''

        '''
        RESET test for specification (squares and cubes)
        Test statistic: F = 5.219019,
        with p-value = P(F(2,197) > 5.21902) = 0.00619

        RESET test for specification (squares only)
        Test statistic: F = 7.268492,
        with p-value = P(F(1,198) > 7.26849) = 0.00762

        RESET test for specification (cubes only)
        Test statistic: F = 5.248951,
        with p-value = P(F(1,198) > 5.24895) = 0.023:
        '''

        '''
        Test for ARCH of order 4

                     coefficient   std. error   t-ratio   p-value
          --------------------------------------------------------
          alpha(0)   97.0386       20.3234       4.775    3.56e-06 ***
          alpha(1)    0.176114      0.0714698    2.464    0.0146   **
          alpha(2)   -0.0488339     0.0724981   -0.6736   0.5014
          alpha(3)   -0.0705413     0.0737058   -0.9571   0.3397
          alpha(4)    0.0384531     0.0725763    0.5298   0.5968

          Null hypothesis: no ARCH effect is present
          Test statistic: LM = 7.30776
          with p-value = P(Chi-square(4) > 7.30776) = 0.120491:
        '''

        '''
        Variance Inflation Factors

        Minimum possible value = 1.0
        Values > 10.0 may indicate a collinearity problem

           ds_l_realgdp    1.002
              realint_1    1.002

        VIF(j) = 1/(1 - R(j)^2), where R(j) is the multiple correlation coefficient
        between variable j and the other independent variables

        Properties of matrix X'X:

         1-norm = 6862.0664
         Determinant = 1.0296049e+009
         Reciprocal condition number = 0.013819244
        '''
        '''
        Test for ARCH of order 4 -
          Null hypothesis: no ARCH effect is present
          Test statistic: LM = 7.30776
          with p-value = P(Chi-square(4) > 7.30776) = 0.120491

        Test of common factor restriction -
          Null hypothesis: restriction is acceptable
          Test statistic: F(2, 195) = 0.426391
          with p-value = P(F(2, 195) > 0.426391) = 0.653468

        Test for normality of residual -
          Null hypothesis: error is normally distributed
          Test statistic: Chi-square(2) = 20.2792
          with p-value = 3.94837e-005:
        '''

        #no idea what this is
        '''
        Augmented regression for common factor test
        OLS, using observations 1959:3-2009:3 (T = 201)
        Dependent variable: ds_l_realinv

                           coefficient   std. error   t-ratio    p-value
          ---------------------------------------------------------------
          const            -10.9481      1.35807      -8.062    7.44e-014 ***
          ds_l_realgdp       4.28893     0.229459     18.69     2.40e-045 ***
          realint_1         -0.662644    0.334872     -1.979    0.0492    **
          ds_l_realinv_1    -0.108892    0.0715042    -1.523    0.1294
          ds_l_realgdp_1     0.660443    0.390372      1.692    0.0923    *
          realint_2          0.0769695   0.341527      0.2254   0.8219

          Sum of squared residuals = 22432.8

        Test of common factor restriction

          Test statistic: F(2, 195) = 0.426391, with p-value = 0.653468
        '''


        ################ with OLS, HAC errors

        #Model 5: OLS, using observations 1959:2-2009:3 (T = 202)
        #Dependent variable: ds_l_realinv
        #HAC standard errors, bandwidth 4 (Bartlett kernel)

        #coefficient   std. error   t-ratio    p-value 95% CONFIDENCE INTERVAL
        #for confidence interval t(199, 0.025) = 1.972

        partable = np.array([
        [-9.48167,      1.17709,     -8.055,    7.17e-014, -11.8029, -7.16049], # ***
        [4.37422,      0.328787,    13.30,     2.62e-029, 3.72587, 5.02258], #***
        [-0.613997,     0.293619,    -2.091,    0.0378, -1.19300, -0.0349939]]) # **

        result_gretl_g1 = dict(
                    endog_mean = ("Mean dependent var",   3.257395),
                    endog_std = ("S.D. dependent var",   18.73915),
                    ssr = ("Sum squared resid",    22799.68),
                    mse_resid_sqrt = ("S.E. of regression",   10.70380),
                    rsquared = ("R-squared",            0.676978),
                    rsquared_adj = ("Adjusted R-squared",   0.673731),
                    fvalue = ("F(2, 199)",            90.79971),
                    f_pvalue = ("P-value(F)",           9.53e-29),
                    llf = ("Log-likelihood",      -763.9752),
                    aic = ("Akaike criterion",     1533.950),
                    bic = ("Schwarz criterion",    1543.875),
                    hqic = ("Hannan-Quinn",         1537.966),
                    resid_acf1 = ("rho",                 -0.107341),
                    dw = ("Durbin-Watson",        2.213805))

        linear_logs = [1.68351, 0.430953, 2, "chi2"]
        #for logs: dropping 70 nan or incomplete observations, T=133
        #(res_ols.model.exog <=0).any(1).sum() = 69  ?not 70
        linear_squares = [7.52477, 0.0232283, 2, "chi2"]

        #Autocorrelation, Breusch-Godfrey test for autocorrelation up to order 4
        lm_acorr4 = [1.17928, 0.321197, 4, 195, "F"]
        lm2_acorr4 = [4.771043, 0.312, 4, "chi2"]
        acorr_ljungbox4 = [5.23587, 0.264, 4, "chi2"]

        #break
        cusum_Harvey_Collier  = [0.494432, 0.621549, 198, "t"] #stats.t.sf(0.494432, 198)*2
        #see cusum results in files
        break_qlr = [3.01985, 0.1, 3, 196, "maxF"]  #TODO check this, max at 2001:4
        break_chow = [13.1897, 0.00424384, 3, "chi2"] # break at 1984:1

        arch_4 = [3.43473, 0.487871, 4, "chi2"]

        normality = [23.962, 0.00001, 2, "chi2"]

        het_white = [33.503723, 0.000003, 5, "chi2"]
        het_breush_pagan = [1.302014, 0.521520, 2, "chi2"]  #TODO: not available
        het_breush_pagan_konker = [0.709924, 0.701200, 2, "chi2"]


        reset_2_3 = [5.219019, 0.00619, 2, 197, "f"]
        reset_2 = [7.268492, 0.00762, 1, 198, "f"]
        reset_3 = [5.248951, 0.023, 1, 198, "f"]  #not available

        cond_1norm = 5984.0525
        determinant = 7.1087467e+008
        reciprocal_condition_number = 0.013826504
        vif = [1.001, 1.001]

        names = 'date   residual        leverage       influence        DFFITS'.split()
        cur_dir = os.path.abspath(os.path.dirname(__file__))
        fpath = os.path.join(cur_dir, 'results/leverage_influence_ols_nostars.txt')
        lev = np.genfromtxt(fpath, skip_header=3, skip_footer=1,
                            converters={0:lambda s: s})
        #either numpy 1.6 or python 3.2 changed behavior
        if np.isnan(lev[-1]['f1']):
            lev = np.genfromtxt(fpath, skip_header=3, skip_footer=2,
                                converters={0:lambda s: s})

        lev.dtype.names = names

        res = res_ols #for easier copying

        cov_hac = sw.cov_hac_simple(res, nlags=4, use_correction=False)
        bse_hac =  sw.se_cov(cov_hac)

        assert_almost_equal(res.params, partable[:,0], 5)
        assert_almost_equal(bse_hac, partable[:,1], 5)
        #TODO

        assert_almost_equal(res.ssr, result_gretl_g1['ssr'][1], decimal=2)
        assert_almost_equal(res.llf, result_gretl_g1['llf'][1], decimal=4) #not in gretl
        assert_almost_equal(res.rsquared, result_gretl_g1['rsquared'][1], decimal=6) #FAIL
        assert_almost_equal(res.rsquared_adj, result_gretl_g1['rsquared_adj'][1], decimal=6) #FAIL
        assert_almost_equal(np.sqrt(res.mse_resid), result_gretl_g1['mse_resid_sqrt'][1], decimal=5)
        #f-value is based on cov_hac I guess
        #res2 = res.get_robustcov_results(cov_type='HC1')
        # TODO: fvalue differs from Gretl, trying any of the HCx
        #assert_almost_equal(res2.fvalue, result_gretl_g1['fvalue'][1], decimal=0) #FAIL
        #assert_approx_equal(res.f_pvalue, result_gretl_g1['f_pvalue'][1], significant=1) #FAIL
        #assert_almost_equal(res.durbin_watson, result_gretl_g1['dw'][1], decimal=7) #TODO


        c = oi.reset_ramsey(res, degree=2)
        compare_ftest(c, reset_2, decimal=(6,5))
        c = oi.reset_ramsey(res, degree=3)
        compare_ftest(c, reset_2_3, decimal=(6,5))

        linear_sq = smsdia.linear_lm(res.resid, res.model.exog)
        assert_almost_equal(linear_sq[0], linear_squares[0], decimal=6)
        assert_almost_equal(linear_sq[1], linear_squares[1], decimal=7)

        hbpk = smsdia.het_breushpagan(res.resid, res.model.exog)
        assert_almost_equal(hbpk[0], het_breush_pagan_konker[0], decimal=6)
        assert_almost_equal(hbpk[1], het_breush_pagan_konker[1], decimal=6)

        hw = smsdia.het_white(res.resid, res.model.exog)
        assert_almost_equal(hw[:2], het_white[:2], 6)

        #arch
        #sm_arch = smsdia.acorr_lm(res.resid**2, maxlag=4, autolag=None)
        sm_arch = smsdia.het_arch(res.resid, maxlag=4)
        assert_almost_equal(sm_arch[0], arch_4[0], decimal=5)
        assert_almost_equal(sm_arch[1], arch_4[1], decimal=6)

        vif2 = [oi.variance_inflation_factor(res.model.exog, k) for k in [1,2]]

        infl = oi.OLSInfluence(res_ols)
        #print np.max(np.abs(lev['DFFITS'] - infl.dffits[0]))
        #print np.max(np.abs(lev['leverage'] - infl.hat_matrix_diag))
        #print np.max(np.abs(lev['influence'] - infl.influence))  #just added this based on Gretl

        #just rough test, low decimal in Gretl output,
        assert_almost_equal(lev['residual'], res.resid, decimal=3)
        assert_almost_equal(lev['DFFITS'], infl.dffits[0], decimal=3)
        assert_almost_equal(lev['leverage'], infl.hat_matrix_diag, decimal=3)
        assert_almost_equal(lev['influence'], infl.influence, decimal=4)

def test_GLSARlag():
    #test that results for lag>1 is close to lag=1, and smaller ssr

    from statsmodels.datasets import macrodata
    d2 = macrodata.load().data
    g_gdp = 400*np.diff(np.log(d2['realgdp']))
    g_inv = 400*np.diff(np.log(d2['realinv']))
    exogg = add_constant(np.c_[g_gdp, d2['realint'][:-1]], prepend=False)

    mod1 = GLSAR(g_inv, exogg, 1)
    res1 = mod1.iterative_fit(5)

    mod4 = GLSAR(g_inv, exogg, 4)
    res4 = mod4.iterative_fit(10)

    assert_array_less(np.abs(res1.params / res4.params - 1), 0.03)
    assert_array_less(res4.ssr, res1.ssr)
    assert_array_less(np.abs(res4.bse / res1.bse) - 1, 0.015)
    assert_array_less(np.abs((res4.fittedvalues / res1.fittedvalues - 1).mean()),
                      0.015)
    assert_equal(len(mod4.rho), 4)




if __name__ == '__main__':
    t = TestGLSARGretl()
    t.test_all()


'''
Model 5: OLS, using observations 1959:2-2009:3 (T = 202)
Dependent variable: ds_l_realinv
HAC standard errors, bandwidth 4 (Bartlett kernel)

                 coefficient   std. error   t-ratio    p-value
  -------------------------------------------------------------
  const           -9.48167      1.17709     -8.055    7.17e-014 ***
  ds_l_realgdp     4.37422      0.328787    13.30     2.62e-029 ***
  realint_1       -0.613997     0.293619    -2.091    0.0378    **

Mean dependent var   3.257395   S.D. dependent var   18.73915
Sum squared resid    22799.68   S.E. of regression   10.70380
R-squared            0.676978   Adjusted R-squared   0.673731
F(2, 199)            90.79971   P-value(F)           9.53e-29
Log-likelihood      -763.9752   Akaike criterion     1533.950
Schwarz criterion    1543.875   Hannan-Quinn         1537.966
rho                 -0.107341   Durbin-Watson        2.213805

QLR test for structural break -
  Null hypothesis: no structural break
  Test statistic: max F(3, 196) = 3.01985 at observation 2001:4
  (10 percent critical value = 4.09)

Non-linearity test (logs) -
  Null hypothesis: relationship is linear
  Test statistic: LM = 1.68351
  with p-value = P(Chi-square(2) > 1.68351) = 0.430953

Non-linearity test (squares) -
  Null hypothesis: relationship is linear
  Test statistic: LM = 7.52477
  with p-value = P(Chi-square(2) > 7.52477) = 0.0232283

LM test for autocorrelation up to order 4 -
  Null hypothesis: no autocorrelation
  Test statistic: LMF = 1.17928
  with p-value = P(F(4,195) > 1.17928) = 0.321197

CUSUM test for parameter stability -
  Null hypothesis: no change in parameters
  Test statistic: Harvey-Collier t(198) = 0.494432
  with p-value = P(t(198) > 0.494432) = 0.621549

Chow test for structural break at observation 1984:1 -
  Null hypothesis: no structural break
  Asymptotic test statistic: Chi-square(3) = 13.1897
  with p-value = 0.00424384

Test for ARCH of order 4 -
  Null hypothesis: no ARCH effect is present
  Test statistic: LM = 3.43473
  with p-value = P(Chi-square(4) > 3.43473) = 0.487871:

#ANOVA
Analysis of Variance:

                     Sum of squares       df      Mean square

  Regression                47782.7        2          23891.3
  Residual                  22799.7      199          114.571
  Total                     70582.3      201          351.156

  R^2 = 47782.7 / 70582.3 = 0.676978
  F(2, 199) = 23891.3 / 114.571 = 208.528 [p-value 1.47e-049]

#LM-test autocorrelation
Breusch-Godfrey test for autocorrelation up to order 4
OLS, using observations 1959:2-2009:3 (T = 202)
Dependent variable: uhat

                 coefficient   std. error   t-ratio    p-value
  ------------------------------------------------------------
  const           0.0640964    1.06719       0.06006   0.9522
  ds_l_realgdp   -0.0456010    0.217377     -0.2098    0.8341
  realint_1       0.0511769    0.293136      0.1746    0.8616
  uhat_1         -0.104707     0.0719948    -1.454     0.1475
  uhat_2         -0.00898483   0.0742817    -0.1210    0.9039
  uhat_3          0.0837332    0.0735015     1.139     0.2560
  uhat_4         -0.0636242    0.0737363    -0.8629    0.3893

  Unadjusted R-squared = 0.023619

Test statistic: LMF = 1.179281,
with p-value = P(F(4,195) > 1.17928) = 0.321

Alternative statistic: TR^2 = 4.771043,
with p-value = P(Chi-square(4) > 4.77104) = 0.312

Ljung-Box Q' = 5.23587,
with p-value = P(Chi-square(4) > 5.23587) = 0.264:

RESET test for specification (squares and cubes)
Test statistic: F = 5.219019,
with p-value = P(F(2,197) > 5.21902) = 0.00619

RESET test for specification (squares only)
Test statistic: F = 7.268492,
with p-value = P(F(1,198) > 7.26849) = 0.00762

RESET test for specification (cubes only)
Test statistic: F = 5.248951,
with p-value = P(F(1,198) > 5.24895) = 0.023

#heteroscedasticity White
White's test for heteroskedasticity
OLS, using observations 1959:2-2009:3 (T = 202)
Dependent variable: uhat^2

                  coefficient   std. error   t-ratio   p-value
  -------------------------------------------------------------
  const           104.920       21.5848       4.861    2.39e-06 ***
  ds_l_realgdp    -29.7040       6.24983     -4.753    3.88e-06 ***
  realint_1        -6.93102      6.95607     -0.9964   0.3203
  sq_ds_l_realg     4.12054      0.684920     6.016    8.62e-09 ***
  X2_X3             2.89685      1.38571      2.091    0.0379   **
  sq_realint_1      0.662135     1.10919      0.5970   0.5512

  Unadjusted R-squared = 0.165860

Test statistic: TR^2 = 33.503723,
with p-value = P(Chi-square(5) > 33.503723) = 0.000003:

#heteroscedasticity Breusch-Pagan (original)
Breusch-Pagan test for heteroskedasticity
OLS, using observations 1959:2-2009:3 (T = 202)
Dependent variable: scaled uhat^2

                 coefficient   std. error   t-ratio    p-value
  -------------------------------------------------------------
  const           1.09468      0.192281      5.693     4.43e-08 ***
  ds_l_realgdp   -0.0323119    0.0386353    -0.8363    0.4040
  realint_1       0.00410778   0.0512274     0.08019   0.9362

  Explained sum of squares = 2.60403

Test statistic: LM = 1.302014,
with p-value = P(Chi-square(2) > 1.302014) = 0.521520

#heteroscedasticity Breusch-Pagan Koenker
Breusch-Pagan test for heteroskedasticity
OLS, using observations 1959:2-2009:3 (T = 202)
Dependent variable: scaled uhat^2 (Koenker robust variant)

                 coefficient   std. error   t-ratio    p-value
  ------------------------------------------------------------
  const           10.6870       21.7027      0.4924    0.6230
  ds_l_realgdp    -3.64704       4.36075    -0.8363    0.4040
  realint_1        0.463643      5.78202     0.08019   0.9362

  Explained sum of squares = 33174.2

Test statistic: LM = 0.709924,
with p-value = P(Chi-square(2) > 0.709924) = 0.701200

########## forecast
#forecast mean y
 For 95% confidence intervals, t(199, 0.025) = 1.972

     Obs ds_l_realinv    prediction    std. error        95% interval

  2008:3     -7.134492   -17.177905     2.946312   -22.987904 - -11.367905
  2008:4    -27.665860   -36.294434     3.036851   -42.282972 - -30.305896
  2009:1    -70.239280   -44.018178     4.007017   -51.919841 - -36.116516
  2009:2    -27.024588   -12.284842     1.427414   -15.099640 - -9.470044
  2009:3      8.078897     4.483669     1.315876     1.888819 - 7.078520

  Forecast evaluation statistics

  Mean Error                       -3.7387
  Mean Squared Error                218.61
  Root Mean Squared Error           14.785
  Mean Absolute Error               12.646
  Mean Percentage Error            -7.1173
  Mean Absolute Percentage Error   -43.867
  Theil's U                         0.4365
  Bias proportion, UM               0.06394
  Regression proportion, UR         0.13557
  Disturbance proportion, UD        0.80049

#forecast actual y
 For 95% confidence intervals, t(199, 0.025) = 1.972

     Obs ds_l_realinv    prediction    std. error        95% interval

  2008:3     -7.134492   -17.177905    11.101892   -39.070353 - 4.714544
  2008:4    -27.665860   -36.294434    11.126262   -58.234939 - -14.353928
  2009:1    -70.239280   -44.018178    11.429236   -66.556135 - -21.480222
  2009:2    -27.024588   -12.284842    10.798554   -33.579120 - 9.009436
  2009:3      8.078897     4.483669    10.784377   -16.782652 - 25.749991

  Forecast evaluation statistics

  Mean Error                       -3.7387
  Mean Squared Error                218.61
  Root Mean Squared Error           14.785
  Mean Absolute Error               12.646
  Mean Percentage Error            -7.1173
  Mean Absolute Percentage Error   -43.867
  Theil's U                         0.4365
  Bias proportion, UM               0.06394
  Regression proportion, UR         0.13557
  Disturbance proportion, UD        0.80049

'''
