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model.py
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model.py
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import numpy as np
from scipy import optimize, stats
from statsmodels.base.data import handle_data
from statsmodels.tools.tools import recipr
from statsmodels.stats.contrast import ContrastResults
from statsmodels.tools.decorators import (resettable_cache,
cache_readonly)
import statsmodels.base.wrapper as wrap
from statsmodels.sandbox.regression.numdiff import approx_fprime1
class Model(object):
"""
A (predictive) statistical model. The class Model itself is not to be used.
Model lays out the methods expected of any subclass.
Parameters
----------
endog : array-like
Endogenous response variable.
exog : array-like
Exogenous design.
Notes
-----
`endog` and `exog` are references to any data provided. So if the data is
already stored in numpy arrays and it is changed then `endog` and `exog`
will change as well.
"""
def __init__(self, endog, exog=None):
self._data = handle_data(endog, exog)
self.exog = self._data.exog
self.endog = self._data.endog
self._data_attr = []
self._data_attr.extend(['exog', 'endog', '_data.exog', '_data.endog',
'_data._orig_endog', '_data._orig_exog'])
@property
def endog_names(self):
return self._data.ynames
@property
def exog_names(self):
return self._data.xnames
def fit(self):
"""
Fit a model to data.
"""
raise NotImplementedError
def predict(self, params, exog=None, *args, **kwargs):
"""
After a model has been fit predict returns the fitted values.
This is a placeholder intended to be overwritten by individual models.
"""
raise NotImplementedError
class LikelihoodModel(Model):
"""
Likelihood model is a subclass of Model.
"""
def __init__(self, endog, exog=None):
super(LikelihoodModel, self).__init__(endog, exog)
self.initialize()
def initialize(self):
"""
Initialize (possibly re-initialize) a Model instance. For
instance, the design matrix of a linear model may change
and some things must be recomputed.
"""
pass
# TODO: if the intent is to re-initialize the model with new data then this
# method needs to take inputs...
def loglike(self, params):
"""
Log-likelihood of model.
"""
raise NotImplementedError
def score(self, params):
"""
Score vector of model.
The gradient of logL with respect to each parameter.
"""
raise NotImplementedError
def information(self, params):
"""
Fisher information matrix of model
Returns -Hessian of loglike evaluated at params.
"""
raise NotImplementedError
def hessian(self, params):
"""
The Hessian matrix of the model
"""
raise NotImplementedError
def fit(self, start_params=None, method='newton', maxiter=100,
full_output=True, disp=True, fargs=(), callback=None, retall=False,
**kwargs):
"""
Fit method for likelihood based models
Parameters
----------
start_params : array-like, optional
Initial guess of the solution for the loglikelihood maximization.
The default is an array of zeros.
method : str {'newton','nm','bfgs','powell','cg', or 'ncg'}
Method can be 'newton' for Newton-Raphson, 'nm' for Nelder-Mead,
'bfgs' for Broyden-Fletcher-Goldfarb-Shanno, 'powell' for modified
Powell's method, 'cg' for conjugate gradient, or 'ncg' for Newton-
conjugate gradient. `method` determines which solver from
scipy.optimize is used. The explicit arguments in `fit` are passed
to the solver. Each solver has several optional arguments that are
not the same across solvers. See the notes section below (or
scipy.optimize) for the available arguments.
maxiter : int
The maximum number of iterations to perform.
full_output : bool
Set to True to have all available output in the Results object's
mle_retvals attribute. The output is dependent on the solver.
See LikelihoodModelResults notes section for more information.
disp : bool
Set to True to print convergence messages.
fargs : tuple
Extra arguments passed to the likelihood function, i.e.,
loglike(x,*args)
callback : callable callback(xk)
Called after each iteration, as callback(xk), where xk is the
current parameter vector.
retall : bool
Set to True to return list of solutions at each iteration.
Available in Results object's mle_retvals attribute.
Notes
-----
Optional arguments for the solvers (available in Results.mle_settings):
'newton'
tol : float
Relative error in params acceptable for convergence.
'nm' -- Nelder Mead
xtol : float
Relative error in params acceptable for convergence
ftol : float
Relative error in loglike(params) acceptable for
convergence
maxfun : int
Maximum number of function evaluations to make.
'bfgs'
gtol : float
Stop when norm of gradient is less than gtol.
norm : float
Order of norm (np.Inf is max, -np.Inf is min)
epsilon
If fprime is approximated, use this value for the step
size. Only relevant if LikelihoodModel.score is None.
'cg'
gtol : float
Stop when norm of gradient is less than gtol.
norm : float
Order of norm (np.Inf is max, -np.Inf is min)
epsilon : float
If fprime is approximated, use this value for the step
size. Can be scalar or vector. Only relevant if
Likelihoodmodel.score is None.
'ncg'
fhess_p : callable f'(x,*args)
Function which computes the Hessian of f times an arbitrary
vector, p. Should only be supplied if
LikelihoodModel.hessian is None.
avextol : float
Stop when the average relative error in the minimizer
falls below this amount.
epsilon : float or ndarray
If fhess is approximated, use this value for the step size.
Only relevant if Likelihoodmodel.hessian is None.
'powell'
xtol : float
Line-search error tolerance
ftol : float
Relative error in loglike(params) for acceptable for
convergence.
maxfun : int
Maximum number of function evaluations to make.
start_direc : ndarray
Initial direction set.
"""
Hinv = None # JP error if full_output=0, Hinv not defined
methods = ['newton', 'nm', 'bfgs', 'powell', 'cg', 'ncg']
if start_params is None:
if hasattr(self, 'start_params'):
start_params = self.start_params
elif self.exog is not None:
# fails for shape (K,)?
start_params = [0] * self.exog.shape[1]
else:
raise ValueError("If exog is None, then start_params should "
"be specified")
if method.lower() not in methods:
raise ValueError("Unknown fit method %s" % method)
method = method.lower()
# TODO: separate args from nonarg taking score and hessian, ie.,
# user-supplied and numerically evaluated estimate frprime doesn't take
# args in most (any?) of the optimize function
f = lambda params, *args: -self.loglike(params, *args)
score = lambda params: -self.score(params)
try:
hess = lambda params: -self.hessian(params)
except:
hess = None
fit_funcs = {
'newton': _fit_mle_newton,
'nm': _fit_mle_nm, # Nelder-Mead
'bfgs': _fit_mle_bfgs,
'cg': _fit_mle_cg,
'ncg': _fit_mle_ncg,
'powell': _fit_mle_powell
}
if method == 'newton':
score = lambda params: self.score(params)
hess = lambda params: self.hessian(params)
func = fit_funcs[method]
xopt, retvals = func(f, score, start_params, fargs, kwargs,
disp=disp, maxiter=maxiter, callback=callback,
retall=retall, full_output=full_output,
hess=hess)
if not full_output:
xopt = retvals
# NOTE: better just to use the Analytic Hessian here, as approximation
# isn't great
# if method == 'bfgs' and full_output:
# Hinv = retvals.setdefault('Hinv', 0)
elif method == 'newton' and full_output:
Hinv = np.linalg.inv(-retvals['Hessian'])
else:
try:
Hinv = np.linalg.inv(-1 * self.hessian(xopt))
except:
#might want custom warning ResultsWarning? NumericalWarning?
from warnings import warn
warndoc = ('Inverting hessian failed, no bse or '
'cov_params available')
warn(warndoc, Warning)
Hinv = None
#TODO: add Hessian approximation and change the above if needed
mlefit = LikelihoodModelResults(self, xopt, Hinv, scale=1.)
#TODO: hardcode scale?
if isinstance(retvals, dict):
mlefit.mle_retvals = retvals
optim_settings = {'optimizer': method, 'start_params': start_params,
'maxiter': maxiter, 'full_output': full_output,
'disp': disp, 'fargs': fargs, 'callback': callback,
'retall': retall}
optim_settings.update(kwargs)
mlefit.mle_settings = optim_settings
return mlefit
def _fit_mle_newton(f, score, start_params, fargs, kwargs, disp=True,
maxiter=100, callback=None, retall=False,
full_output=True, hess=None):
tol = kwargs.setdefault('tol', 1e-8)
iterations = 0
oldparams = np.inf
newparams = np.asarray(start_params)
if retall:
history = [oldparams, newparams]
while (iterations < maxiter and np.any(np.abs(newparams -
oldparams) > tol)):
H = hess(newparams)
oldparams = newparams
newparams = oldparams - np.dot(np.linalg.inv(H),
score(oldparams))
if retall:
history.append(newparams)
if callback is not None:
callback(newparams)
iterations += 1
fval = f(newparams, *fargs) # this is the negative likelihood
if iterations == maxiter:
warnflag = 1
if disp:
print ("Warning: Maximum number of iterations has been "
"exceeded.")
print " Current function value: %f" % fval
print " Iterations: %d" % iterations
else:
warnflag = 0
if disp:
print "Optimization terminated successfully."
print " Current function value: %f" % fval
print " Iterations %d" % iterations
if full_output:
(xopt, fopt, niter,
gopt, hopt) = (newparams, f(newparams, *fargs),
iterations, score(newparams),
hess(newparams))
converged = not warnflag
retvals = {'fopt': fopt, 'iterations': niter, 'score': gopt,
'Hessian': hopt, 'warnflag': warnflag,
'converged': converged}
if retall:
retvals.update({'allvecs': history})
else:
return newparams
return xopt, retvals
def _fit_mle_bfgs(f, score, start_params, fargs, kwargs, disp=True,
maxiter=100, callback=None, retall=False,
full_output=True, hess=None):
gtol = kwargs.setdefault('gtol', 1.0000000000000001e-05)
norm = kwargs.setdefault('norm', np.Inf)
epsilon = kwargs.setdefault('epsilon', 1.4901161193847656e-08)
retvals = optimize.fmin_bfgs(f, start_params, score, args=fargs,
gtol=gtol, norm=norm, epsilon=epsilon,
maxiter=maxiter, full_output=full_output,
disp=disp, retall=retall, callback=callback)
if full_output:
if not retall:
xopt, fopt, gopt, Hinv, fcalls, gcalls, warnflag = retvals
else:
(xopt, fopt, gopt, Hinv, fcalls,
gcalls, warnflag, allvecs) = retvals
converged = not warnflag
retvals = {'fopt': fopt, 'gopt': gopt, 'Hinv': Hinv,
'fcalls': fcalls, 'gcalls': gcalls, 'warnflag':
warnflag, 'converged': converged}
if retall:
retvals.update({'allvecs': allvecs})
return xopt, retvals
def _fit_mle_nm(f, score, start_params, fargs, kwargs, disp=True,
maxiter=100, callback=None, retall=False,
full_output=True, hess=None):
xtol = kwargs.setdefault('xtol', 0.0001)
ftol = kwargs.setdefault('ftol', 0.0001)
maxfun = kwargs.setdefault('maxfun', None)
retvals = optimize.fmin(f, start_params, args=fargs, xtol=xtol,
ftol=ftol, maxiter=maxiter, maxfun=maxfun,
full_output=full_output, disp=disp, retall=retall,
callback=callback)
if full_output:
if not retall:
xopt, fopt, niter, fcalls, warnflag = retvals
else:
xopt, fopt, niter, fcalls, warnflag, allvecs = retvals
converged = not warnflag
retvals = {'fopt': fopt, 'iterations': niter,
'fcalls': fcalls, 'warnflag': warnflag,
'converged': converged}
if retall:
retvals.update({'allvecs': allvecs})
return xopt, retvals
def _fit_mle_cg(f, score, start_params, fargs, kwargs, disp=True,
maxiter=100, callback=None, retall=False,
full_output=True, hess=None):
gtol = kwargs.setdefault('gtol', 1.0000000000000001e-05)
norm = kwargs.setdefault('norm', np.Inf)
epsilon = kwargs.setdefault('epsilon', 1.4901161193847656e-08)
retvals = optimize.fmin_cg(f, start_params, score, gtol=gtol, norm=norm,
epsilon=epsilon, maxiter=maxiter,
full_output=full_output, disp=disp,
retall=retall, callback=callback)
if full_output:
if not retall:
xopt, fopt, fcalls, gcalls, warnflag = retvals
else:
xopt, fopt, fcalls, gcalls, warnflag, allvecs = retvals
converged = not warnflag
retvals = {'fopt': fopt, 'fcalls': fcalls, 'gcalls': gcalls,
'warnflag': warnflag, 'converged': converged}
if retall:
retvals.update({'allvecs': allvecs})
return xopt, retvals
def _fit_mle_ncg(f, score, start_params, fargs, kwargs, disp=True,
maxiter=100, callback=None, retall=False,
full_output=True, hess=None):
fhess_p = kwargs.setdefault('fhess_p', None)
avextol = kwargs.setdefault('avextol', 1.0000000000000001e-05)
epsilon = kwargs.setdefault('epsilon', 1.4901161193847656e-08)
retvals = optimize.fmin_ncg(f, start_params, score, fhess_p=fhess_p,
fhess=hess, args=fargs, avextol=avextol,
epsilon=epsilon, maxiter=maxiter,
full_output=full_output, disp=disp,
retall=retall, callback=callback)
if full_output:
if not retall:
xopt, fopt, fcalls, gcalls, hcalls, warnflag = retvals
else:
xopt, fopt, fcalls, gcalls, hcalls, warnflag, allvecs =\
retvals
converged = not warnflag
retvals = {'fopt': fopt, 'fcalls': fcalls, 'gcalls': gcalls,
'hcalls': hcalls, 'warnflag': warnflag,
'converged': converged}
if retall:
retvals.update({'allvecs': allvecs})
return xopt, retvals
def _fit_mle_powell(f, score, start_params, fargs, kwargs, disp=True,
maxiter=100, callback=None, retall=False,
full_output=True, hess=None):
xtol = kwargs.setdefault('xtol', 0.0001)
ftol = kwargs.setdefault('ftol', 0.0001)
maxfun = kwargs.setdefault('maxfun', None)
start_direc = kwargs.setdefault('start_direc', None)
retvals = optimize.fmin_powell(f, start_params, args=fargs, xtol=xtol,
ftol=ftol, maxiter=maxiter, maxfun=maxfun,
full_output=full_output, disp=disp,
retall=retall, callback=callback,
direc=start_direc)
if full_output:
if not retall:
xopt, fopt, direc, niter, fcalls, warnflag = retvals
else:
xopt, fopt, direc, niter, fcalls, warnflag, allvecs =\
retvals
converged = not warnflag
retvals = {'fopt': fopt, 'direc': direc, 'iterations': niter,
'fcalls': fcalls, 'warnflag': warnflag,
'converged': converged}
if retall:
retvals.update({'allvecs': allvecs})
return xopt, retvals
#TODO: the below is unfinished
class GenericLikelihoodModel(LikelihoodModel):
"""
Allows the fitting of any likelihood function via maximum likelihood.
A subclass needs to specify at least the log-likelihood
If the log-likelihood is specified for each observation, then results that
require the Jacobian will be available. (The other case is not tested yet.)
Notes
-----
Optimization methods that require only a likelihood function are 'nm' and
'powell'
Optimization methods that require a likelihood function and a
score/gradient are 'bfgs', 'cg', and 'ncg'. A function to compute the
Hessian is optional for 'ncg'.
Optimization method that require a likelihood function, a score/gradient,
and a Hessian is 'newton'
If they are not overwritten by a subclass, then numerical gradient,
Jacobian and Hessian of the log-likelihood are caclulated by numerical
forward differentiation. This might results in some cases in precision
problems, and the Hessian might not be positive definite. Even if the
Hessian is not positive definite the covariance matrix of the parameter
estimates based on the outer product of the Jacobian might still be valid.
Examples
--------
see also subclasses in directory miscmodels
import statsmodels.api as sm
data = sm.datasets.spector.load()
data.exog = sm.add_constant(data.exog)
# in this dir
from model import GenericLikelihoodModel
probit_mod = sm.Probit(data.endog, data.exog)
probit_res = probit_mod.fit()
loglike = probit_mod.loglike
score = probit_mod.score
mod = GenericLikelihoodModel(data.endog, data.exog, loglike, score)
res = mod.fit(method="nm", maxiter = 500)
import numpy as np
np.allclose(res.params, probit_res.params)
"""
def __init__(self, endog, exog=None, loglike=None, score=None,
hessian=None):
# let them be none in case user wants to use inheritance
if loglike:
self.loglike = loglike
if score:
self.score = score
if hessian:
self.hessian = hessian
self.confint_dist = stats.norm
# TODO: data structures?
# this won't work for ru2nmnl, maybe np.ndim of a dict?
if exog is not None:
#try:
self.nparams = self.df_model = (exog.shape[1]
if np.ndim(exog) == 2 else 1)
super(GenericLikelihoodModel, self).__init__(endog, exog)
#this is redundant and not used when subclassing
def initialize(self):
if not self.score: # right now score is not optional
self.score = approx_fprime1
if not self.hessian:
pass
else: # can use approx_hess_p if we have a gradient
if not self.hessian:
pass
def expandparams(self, params):
'''
expand to full parameter array when some parameters are fixed
Parameters
----------
params : array
reduced parameter array
Returns
-------
paramsfull : array
expanded parameter array where fixed parameters are included
Notes
-----
Calling this requires that self.fixed_params and self.fixed_paramsmask
are defined.
*developer notes:*
This can be used in the log-likelihood to ...
this could also be replaced by a more general parameter
transformation.
'''
paramsfull = self.fixed_params.copy()
paramsfull[self.fixed_paramsmask] = params
return paramsfull
def reduceparams(self, params):
return params[self.fixed_paramsmask]
def loglike(self, params):
return self.loglikeobs(params).sum(0)
def nloglike(self, params):
return -self.loglikeobs(params).sum(0)
def loglikeobs(self, params):
return -self.nloglikeobs(params)
def score(self, params):
'''
Gradient of log-likelihood evaluated at params
'''
return approx_fprime1(params, self.loglike, epsilon=1e-4).ravel()
def jac(self, params, **kwds):
'''
Jacobian/Gradient of log-likelihood evaluated at params for each
observation.
'''
kwds.setdefault('epsilon', 1e-4)
return approx_fprime1(params, self.loglikeobs, **kwds)
def hessian(self, params):
'''
Hessian of log-likelihood evaluated at params
'''
from statsmodels.sandbox.regression.numdiff import approx_hess
# need options for hess (epsilon)
return approx_hess(params, self.loglike)[0]
def fit(self, start_params=None, method='nm', maxiter=500, full_output=1,
disp=1, callback=None, retall=0, **kwargs):
"""
Fit the model using maximum likelihood.
The rest of the docstring is from
statsmodels.LikelihoodModel.fit
"""
if start_params is None:
if hasattr(self, 'start_params'):
start_params = self.start_params
else:
start_params = 0.1 * np.ones(self.nparams)
fit_method = super(GenericLikelihoodModel, self).fit
mlefit = fit_method(start_params=start_params,
method=method, maxiter=maxiter,
full_output=full_output,
disp=disp, callback=callback, **kwargs)
genericmlefit = GenericLikelihoodModelResults(self, mlefit)
return genericmlefit
#fit.__doc__ += LikelihoodModel.fit.__doc__
#------------------------------
#TODO: the following have been moved to the result mixin class
# check if anything is still using them from here
@cache_readonly
def jacv(self):
if not hasattr(self, '_results'):
raise ValueError('need to call fit first')
return self.jac(self._results.params)
@cache_readonly
def hessv(self):
if not hasattr(self, '_results'):
raise ValueError('need to call fit first')
return self.hessian(self._results.params)
# the following could be moved to results
@cache_readonly
def covjac(self):
'''
covariance of parameters based on loglike outer product of jacobian
'''
## if not hasattr(self, '_results'):
## raise ValueError('need to call fit first')
## #self.fit()
## self.jacv = jacv = self.jac(self._results.params)
jacv = self.jacv
return np.linalg.inv(np.dot(jacv.T, jacv))
@cache_readonly
def covjhj(self):
jacv = self.jacv
## hessv = self.hessv
## hessinv = np.linalg.inv(hessv)
## self.hessinv = hessinv
hessinv = self._results.cov_params()
return np.dot(hessinv, np.dot(np.dot(jacv.T, jacv), hessinv))
@cache_readonly
def bsejhj(self):
return np.sqrt(np.diag(self.covjhj))
@cache_readonly
def bsejac(self):
return np.sqrt(np.diag(self.covjac))
class Results(object):
"""
Class to contain model results
Parameters
----------
model : class instance
the previously specified model instance
params : array
parameter estimates from the fit model
"""
def __init__(self, model, params, **kwd):
self.__dict__.update(kwd)
self.initialize(model, params, **kwd)
self._data_attr = []
def initialize(self, model, params, **kwd):
self.params = params
self.model = model
def predict(self, exog=None, *args, **kwargs):
return self.model.predict(self.params, exog, *args, **kwargs)
#TODO: public method?
class LikelihoodModelResults(Results):
"""
Class to contain results from likelihood models
Parameters
-----------
model : LikelihoodModel instance or subclass instance
LikelihoodModelResults holds a reference to the model that is fit.
params : 1d array_like
parameter estimates from estimated model
normalized_cov_params : 2d array
Normalized (before scaling) covariance of params. (dot(X.T,X))**-1
scale : float
For (some subset of models) scale will typically be the
mean square error from the estimated model (sigma^2)
Returns
-------
**Attributes**
mle_retvals : dict
Contains the values returned from the chosen optimization method if
full_output is True during the fit. Available only if the model
is fit by maximum likelihood. See notes below for the output from
the different methods.
mle_settings : dict
Contains the arguments passed to the chosen optimization method.
Available if the model is fit by maximum likelihood. See
LikelihoodModel.fit for more information.
model : model instance
LikelihoodResults contains a reference to the model that is fit.
params : ndarray
The parameters estimated for the model.
scale : float
The scaling factor of the model given during instantiation.
tvalues : array
The t-values of the standard errors.
Notes
--------
The covariance of params is given by scale times normalized_cov_params.
Return values by solver if full_ouput is True during fit:
'newton'
fopt : float
The value of the (negative) loglikelihood at its
minimum.
iterations : int
Number of iterations performed.
score : ndarray
The score vector at the optimum.
Hessian : ndarray
The Hessian at the optimum.
warnflag : int
1 if maxiter is exceeded. 0 if successful convergence.
converged : bool
True: converged. False: did not converge.
allvecs : list
List of solutions at each iteration.
'nm'
fopt : float
The value of the (negative) loglikelihood at its
minimum.
iterations : int
Number of iterations performed.
warnflag : int
1: Maximum number of function evaluations made.
2: Maximum number of iterations reached.
converged : bool
True: converged. False: did not converge.
allvecs : list
List of solutions at each iteration.
'bfgs'
fopt : float
Value of the (negative) loglikelihood at its minimum.
gopt : float
Value of gradient at minimum, which should be near 0.
Hinv : ndarray
value of the inverse Hessian matrix at minimum. Note
that this is just an approximation and will often be
different from the value of the analytic Hessian.
fcalls : int
Number of calls to loglike.
gcalls : int
Number of calls to gradient/score.
warnflag : int
1: Maximum number of iterations exceeded. 2: Gradient
and/or function calls are not changing.
converged : bool
True: converged. False: did not converge.
allvecs : list
Results at each iteration.
'powell'
fopt : float
Value of the (negative) loglikelihood at its minimum.
direc : ndarray
Current direction set.
iterations : int
Number of iterations performed.
fcalls : int
Number of calls to loglike.
warnflag : int
1: Maximum number of function evaluations. 2: Maximum number
of iterations.
converged : bool
True : converged. False: did not converge.
allvecs : list
Results at each iteration.
'cg'
fopt : float
Value of the (negative) loglikelihood at its minimum.
fcalls : int
Number of calls to loglike.
gcalls : int
Number of calls to gradient/score.
warnflag : int
1: Maximum number of iterations exceeded. 2: Gradient and/
or function calls not changing.
converged : bool
True: converged. False: did not converge.
allvecs : list
Results at each iteration.
'ncg'
fopt : float
Value of the (negative) loglikelihood at its minimum.
fcalls : int
Number of calls to loglike.
gcalls : int
Number of calls to gradient/score.
hcalls : int
Number of calls to hessian.
warnflag : int
1: Maximum number of iterations exceeded.
converged : bool
True: converged. False: did not converge.
allvecs : list
Results at each iteration.
"""
def __init__(self, model, params, normalized_cov_params=None, scale=1.):
super(LikelihoodModelResults, self).__init__(model, params)
self.normalized_cov_params = normalized_cov_params
self.scale = scale
def normalized_cov_params(self):
raise NotImplementedError
#JP: add methods that are valid generically higher up in class hierarchy
@cache_readonly
def llf(self):
return self.model.loglike(self.params)
@cache_readonly
def bse(self):
return np.sqrt(np.diag(self.cov_params()))
def t(self, column=None):
"""
deprecated: Return the t-statistic for a given parameter estimate.
FutureWarning: use attribute tvalues instead, t will be removed
in the next release
Parameters
----------
column : array-like
The columns for which you would like the t-value.
Note that this uses Python's indexing conventions.
See also
---------
Use t_test for more complicated t-statistics.
Examples
--------
>>> import statsmodels.api as sm
>>> data = sm.datasets.longley.load()
>>> data.exog = sm.add_constant(data.exog)
>>> results = sm.OLS(data.endog, data.exog).fit()
>>> results.tvalues
array([ 0.17737603, -1.06951632, -4.13642736, -4.82198531, -0.22605114,
4.01588981, -3.91080292])
>>> results.tvalues[[1,2,4]]
array([-1.06951632, -4.13642736, -0.22605114])
>>> import numpy as np
>>> results.tvalues[np.array([1,2,4]]
array([-1.06951632, -4.13642736, -0.22605114])
"""
import warnings
warnings.warn("`t` will be removed in the next release, use attribute"
"`tvalues` instead", FutureWarning)
if self.normalized_cov_params is None:
raise ValueError('need covariance of parameters for computing T '
'statistics')
if column is None:
column = range(self.params.shape[0])
column = np.asarray(column)
_params = self.params[column]
_cov = self.cov_params(column=column)
if _cov.ndim == 2:
_cov = np.diag(_cov)
_t = _params * recipr(np.sqrt(_cov))
# repicr drops precision for MNLogit?
_t = _params / np.sqrt(_cov)
return _t
@cache_readonly
def tvalues(self):
"""
Return the t-statistic for a given parameter estimate.
"""
return self.params / self.bse
@cache_readonly
def pvalues(self):
return stats.norm.sf(np.abs(self.tvalues)) * 2
def cov_params(self, r_matrix=None, column=None, scale=None, cov_p=None,
other=None):
"""
Returns the variance/covariance matrix.
The variance/covariance matrix can be of a linear contrast
of the estimates of params or all params multiplied by scale which
will usually be an estimate of sigma^2. Scale is assumed to be
a scalar.
Parameters
----------
r_matrix : array-like
Can be 1d, or 2d. Can be used alone or with other.
column : array-like, optional
Must be used on its own. Can be 0d or 1d see below.
scale : float, optional
Can be specified or not. Default is None, which means that
the scale argument is taken from the model.
other : array-like, optional
Can be used when r_matrix is specified.
Returns
-------
(The below are assumed to be in matrix notation.)
cov : ndarray
If no argument is specified returns the covariance matrix of a model
(scale)*(X.T X)^(-1)
If contrast is specified it pre and post-multiplies as follows
(scale) * r_matrix (X.T X)^(-1) r_matrix.T
If contrast and other are specified returns
(scale) * r_matrix (X.T X)^(-1) other.T
If column is specified returns
(scale) * (X.T X)^(-1)[column,column] if column is 0d
OR
(scale) * (X.T X)^(-1)[column][:,column] if column is 1d
"""
if cov_p is None and self.normalized_cov_params is None:
raise ValueError('need covariance of parameters for computing '
'(unnormalized) covariances')
if column is not None and (r_matrix is not None or other is not None):
raise ValueError('Column should be specified without other '
'arguments.')
if other is not None and r_matrix is None:
raise ValueError('other can only be specified with r_matrix')
if cov_p is None:
if scale is None:
scale = self.scale
cov_p = self.normalized_cov_params * scale
if column is not None:
column = np.asarray(column)
if column.shape == ():
return cov_p[column, column]
else:
#return cov_p[column][:, column]
return cov_p[column[:, None], column]
elif r_matrix is not None:
r_matrix = np.asarray(r_matrix)
if r_matrix.shape == ():
raise ValueError("r_matrix should be 1d or 2d")
if other is None:
other = r_matrix
else:
other = np.asarray(other)
tmp = np.dot(r_matrix, np.dot(cov_p, np.transpose(other)))
return tmp
else: #if r_matrix is None and column is None: