refnx.analysis¶
- class refnx.analysis.BaseObjective(p, logl, logp=None, fcn_args=(), fcn_kwds=None, name=None, weighted=True)[source]¶
Bases:
object
Don’t necessarily have to use Parameters, could use np.array
- covar(target='nll')[source]¶
Estimates a covariance matrix based on numerical differentiation of either the negative log-likelihood or negative log-posterior probabilities.
- Parameters
target (str, {"nll", "nlpost"}) –
- Returns
covar – The covariance matrix for the fitting system
- Return type
np.ndarray
Notes
Estimation of a covariance matrix can be susceptible to numeric instabilities. Critically evaluate the matrix before further use.
- logl(pvals=None)[source]¶
Log-likelihood probability function
- Parameters
pvals (np.ndarray) – Array containing the values to be tested.
- Returns
logl – log-likelihood probability.
- Return type
- logp(pvals=None)[source]¶
Log-prior probability function
- Parameters
pvals (np.ndarray) – Array containing the values to be tested.
- Returns
logp – log-prior probability
- Return type
- logpost(pvals=None)[source]¶
Log-posterior probability function
- Parameters
pvals (np.ndarray) – Array containing the values to be tested.
- Returns
logpost – log-probability.
- Return type
Notes
The log probability is the sum is the sum of the log-prior and log-likelihood probabilities. Does not set the parameter attribute.
- nll(pvals=None)[source]¶
Negative log-likelihood function
- Parameters
pvals (np.ndarray) – Array containing the values to be tested.
- Returns
nll – negative log-likelihood
- Return type
- nlpost(pvals=None)[source]¶
Negative log-posterior function
- Parameters
pvals (np.ndarray) – Array containing the values to be tested.
- Returns
nlpost – negative log-posterior
- Return type
- class refnx.analysis.Bounds[source]¶
Bases:
object
A base class that describes the probability distribution for a parameter
- invcdf(q)[source]¶
Calculate the inverse of the cumulative distribution function for the prior.
This is also known as the percent point function, or ppf.
- Parameters
q (array-like) – lower tail probability
- Returns
x – quantile corresponding to the lower tail probability q.
- Return type
array-like
- logp(value)[source]¶
Calculate the log-prior probability of a value with the probability distribution.
- rvs(size=1, random_state=None)[source]¶
Generate random variates from the probability distribution.
- Parameters
size (int or tuple) – Specifies the number, or array shape, of random variates to return.
random_state ({None, int, float or
numpy.random.RandomState
}) – For reproducible sampling
- Returns
arr – Random variates from within the probability distribution.
- Return type
array-like
- class refnx.analysis.CurveFitter(objective, nwalkers=200, ntemps=- 1, **mcmc_kws)[source]¶
Bases:
object
Analyse a curvefitting system (with MCMC sampling)
- Parameters
objective (refnx.analysis.Objective) – The
refnx.analysis.Objective
to be analysed.nwalkers (int, optional) – How many walkers you would like the sampler to have. Must be an even number. The more walkers the better.
ntemps (int or None, optional) – If ntemps == -1, then an
emcee.EnsembleSampler
is used during the sample method. Otherwise, or if ntemps is None then parallel tempering is used with aptemcee.sampler.Sampler
object during the sample method, with ntemps specifing the number of temperatures. Can be None, in which case the Tmax keyword argument sets the maximum temperature. Parallel Tempering is useful if you expect your posterior distribution to be multi-modal.mcmc_kws (dict) – Keywords used to create the
emcee.EnsembleSampler
orptemcee.sampler.Sampler
objects.
Notes
See the documentation at http://dan.iel.fm/emcee/current/api/ for further details on what keywords are permitted, and for further information on Parallel Tempering. The pool and threads keywords are ignored here. Specification of parallel threading is done with the pool argument in the sample method.
- acf(nburn=0, nthin=1)[source]¶
Calculate the autocorrelation function
- Returns
acfs – The autocorrelation function, acfs.shape=(lags, nvary)
- Return type
np.ndarray
- property chain¶
MCMC chain belonging to CurveFitter.sampler
- Returns
chain – The MCMC chain with shape (steps, nwalkers, ndim) or (steps, ntemps, nwalkers, ndim).
- Return type
array
- fit(method='L-BFGS-B', target='nll', verbose=True, **kws)[source]¶
Obtain the maximum log-likelihood, or log-posterior, estimate (mode) of the objective. Maximising the log-likelihood is equivalent to minimising chi2 in a least squares fit.
- Parameters
method (str) –
which method to use for the optimisation. One of:
’least_squares’:
scipy.optimize.least_squares
.’L-BFGS-B’: L-BFGS-B.
’differential_evolution’:
scipy.optimize.differential_evolution
’dual_annealing’:
scipy.optimize.dual_annealing
(SciPy >= 1.2.0)’shgo’:
scipy.optimize.shgo
(SciPy >= 1.2.0)
You can also choose many of the minimizers from
scipy.optimize.minimize
.target ({'nll', 'nlpost'}, optional) – Minimize the negative log-likelihood (‘nll’) or the negative log-posterior (‘nlpost’). This is equivalent to maximising the likelihood or posterior probabilities respectively. Maximising the likelihood is equivalent to minimising chi^2 in a least-squares fit. This option only applies to the differential_evolution, shgo, dual_annealing or L-BFGS-B methods. These optimisers require lower and upper (box) bounds for each parameter. If the Bounds on a parameter are not an Interval, but a PDF specifying a statistical distribution, then the lower and upper bounds are approximated as
PDF.rv.ppf([0.005, 0.995])
, covering 99 % of the statistical distribution.verbose (bool, optional) – Gives fitting progress. To see a progress bar tqdm has to be installed.
kws (dict) – Additional arguments are passed to the underlying minimization method.
- Returns
result, covar – result.x contains the best fit parameters result.covar is the covariance matrix for the fit. result.stderr is the uncertainties on each of the fit parameters.
- Return type
scipy.optimize.OptimizeResult
, np.ndarray
Notes
If the objective supplies a residuals method then least_squares can be used. Otherwise the nll method of the objective is minimised. Use this method just before a sampling run. If self.objective.parameters is a Parameters instance, then each of the varying parameters has its value updated by the fit, and each Parameter has a stderr attribute which represents the uncertainty on the fit parameter.
The use of dual annealing and shgo requires that scipy >= 1.2.0 be installed.
- property index_max_prob¶
The index of the highest log-probability for the samples
- initialise(pos='covar', random_state=None)[source]¶
Initialise the emcee walkers.
- Parameters
pos (str or np.ndarray) –
Method for initialising the emcee walkers. One of:
’covar’, use the estimated covariance of the system.
’jitter’, add a small amount of gaussian noise to each parameter
- ’prior’, sample random locations from the prior using Latin
Hyper Cube.
- pos, an array that specifies a snapshot of the walkers. Has shape
- (nwalkers, ndim), or (ntemps, nwalkers, ndim) if parallel
tempering is employed. You can also provide a previously created chain.
random_state ({int, np.random.RandomState, np.random.Generator}) – If random_state is not specified the ~np.random.RandomState singleton is used. If random_state is an int, a new
RandomState
instance is used, seeded with random_state. If random_state is already aRandomState
or aGenerator
instance, then that object is used. Specify random_state for repeatable initialisations.
- initialise_with_chain(chain)[source]¶
Initialise sampler with a pre-existing chain
- Parameters
chain (array) – Array of size (steps, ntemps, nwalkers, ndim) or (steps, nwalkers, ndim), containing a chain from a previous sampling run.
- property logpost¶
Log-probability for each of the entries in self.chain
- make_sampler()[source]¶
Make the samplers for the Objective.
Use this method if the number of varying parameters changes.
- property nvary¶
- sample(steps, nthin=1, random_state=None, f=None, callback=None, verbose=True, pool=- 1)[source]¶
Performs sampling from the objective.
- Parameters
steps (int) – Collect steps samples into the chain. The sampler will run a total of steps * nthin moves.
nthin (int, optional) – Each chain sample is separated by nthin iterations.
random_state ({int, np.random.RandomState, np.random.Generator}) – If random_state is not specified the ~np.random.RandomState singleton is used. If random_state is an int, a new
RandomState
instance is used, seeded with random_state. If random_state is already aRandomState
or aGenerator
instance, then that object is used. Specify random_state for repeatable minimizations.f (file-like or str) – File to incrementally save chain progress to. Each row in the file is a flattened array of size (nwalkers, ndim) or (ntemps, nwalkers, ndim). There are steps rows in the file.
callback (callable) – callback function to be called at each iteration step. Has the signature callback(coords, logprob).
verbose (bool, optional) – Gives updates on the sampling progress
pool (int or map-like object, optional) – If pool is an int then it specifies the number of threads to use for parallelization. If pool == -1, then all CPU’s are used. If pool is a map-like callable that follows the same calling sequence as the built-in map function, then this pool is used for parallelisation.
Notes
Please see
emcee.EnsembleSampler
for its detailed behaviour.>>> # we'll burn the first 500 steps >>> fitter.sample(500) >>> # after you've run those, then discard them by resetting the >>> # sampler. >>> fitter.sampler.reset() >>> # Now collect 40 steps, each step separated by 50 sampler >>> # generations. >>> fitter.sample(40, nthin=50)
One can also burn and thin in Curvefitter.process_chain.
- class refnx.analysis.GlobalObjective(objectives)[source]¶
Bases:
refnx.analysis.objective.Objective
Global Objective function for simultaneous fitting with refnx.analysis.CurveFitter
- Parameters
objectives (list) – list of
refnx.analysis.Objective
objects
- logl(pvals=None)[source]¶
Calculate the log-likelhood of the system
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
logl – log-likelihood probability
- Return type
- logp(pvals=None)[source]¶
Calculate the log-prior of the system
- Parameters
pvals (array-like or refnx.analysis.Parameters, optional) – values for the varying or entire set of parameters
- Returns
logp – log-prior probability
- Return type
- property npoints¶
int number of data points in all the objectives.
- property parameters¶
refnx.analysis.Parameters
associated with all the objectives.
- plot(pvals=None, samples=0, parameter=None, fig=None)[source]¶
Plot the data/model for all the objectives in the GlobalObjective.
Matplotlib must be installed to use this method.
- Parameters
pvals (np.ndarray, optional) – Numeric values for the Parameter’s that are varying
samples (number, optional) – If the objective has been sampled, how many samples you wish to plot on the graph.
parameter (refnx.analysis.Parameter, optional) – Creates an interactive plot for the Parameter in Jupyter. Requires ipywidgets be installed. Use with %matplotlib notebook/qt.
fig (Figure instance, optional) – If fig is not supplied then a new figure is created. Otherwise the graph is created on the current axes on the supplied figure.
- Returns
fig, ax – matplotlib figure and axes objects.
- Return type
matplotlib.Figure
,matplotlib.Axes
- residuals(pvals=None)[source]¶
Concatenated residuals for each of the
refnx.analysis.Objective.residuals
.- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
residuals – Concatenated
refnx.analysis.Objective.residuals
- Return type
np.ndarray
- property weighted¶
bool do all the datasets have y_err, and are all the objectives wanting to use weights?
- class refnx.analysis.Interval(lb=- inf, ub=inf)[source]¶
Bases:
refnx.analysis.bounds.Bounds
Describes a uniform probability distribution. May be open, semi-open, or closed.
Examples
>>> from refnx.analysis import Parameter, Interval >>> p = Parameter(1) >>> # closed interval >>> p.bounds = Interval(0, 10) >>> p.logp([5, -1]) array([-2.30258509, -inf])
A semi-closed interval will still prevent the fitter from accessing impossible locations.
>>> p.bounds = Interval(lb=-10) >>> p.logp([5, -1]) array([0., 0.])
- invcdf(q)[source]¶
Calculate the inverse of the cumulative distribution function for the uniform prior.
This is also known as the percent point function, or ppf.
- Parameters
q (array-like) – lower tail probability
- Returns
x – quantile corresponding to the lower tail probability q.
- Return type
array-like
- property lb¶
Lower bound of uniform distribution
- property rv¶
- rvs(size=1, random_state=None)[source]¶
Generate random variates from the probability distribution.
- Parameters
size (int or tuple) – Specifies the number, or array shape, of random variates to return.
random_state ({None, int, float or
numpy.random.RandomState
}) – For reproducible sampling
- Returns
arr – Random variates from within the probability distribution.
- Return type
array-like
- property ub¶
Upper bound of uniform distribution
- valid(val)[source]¶
Checks whether a parameter value is within the support of the Interval. If it isn’t then it returns a value that is within the support. If the Interval is closed (i.e. lower and upper bounds are both specified) then invalid values will be corrected by random samples taken between the lower and upper bounds. If the interval is semi-open, only one of the bounds being specified, then invalid values will be corrected by the value being reflected by the same distance from the relevant limit.
- Parameters
val (array-like) – values to examine
- Returns
valid – values within the support
- Return type
array-like
Examples
>>> b = Interval(0, 10) >>> b.valid(11.5) 8.5
- class refnx.analysis.MCMCResult(name, param, stderr, chain, median)¶
Bases:
tuple
- chain¶
Alias for field number 3
- median¶
Alias for field number 4
- name¶
Alias for field number 0
- param¶
Alias for field number 1
- stderr¶
Alias for field number 2
- class refnx.analysis.Model(parameters, fitfunc=None, fcn_args=(), fcn_kwds=None)[source]¶
Bases:
object
Calculates a generative model (dependent variable), given parameters and independent variables.
- Parameters
parameters (array or refnx.analysis.Parameters) – Parameters to calculate the model with
fitfunc (callable, optional) – A function that calculates the generative model. Should have the signature
fitfunc(x, parameters, *fcn_args, **fcn__kwds)
where x is an array-like specifying the independent variables, and parameters are the parameters required to calculate the model. fcn_args and fcn_kwds can be used to supply additional arguments to to fitfunc.fcn_args (sequence, optional) – Supplies extra arguments to fitfunc
fcn_kwds (dict, optional) – Supplies keyword arguments to fitfunc
Notes
It is not necessary to supply fitfunc to create a Model iff you are inheriting Model and are also overriding Model.model.
- property fitfunc¶
The fit-function associated with the model
- logp()[source]¶
The model can add additional terms to it’s log-probability. However, it should _not_ include logp from any of the parameters. That is calculated by Objective.logp.
- model(x, p=None, x_err=None)[source]¶
Calculates a generative model(dependent variable), given parameters and independent variables.
- Parameters
x (array-like) – Independent variable.
p (array-like or refnx.analysis.Parameters) – Parameters to supply to the generative function.
x_err (optional) – Uncertainty in x.
- Returns
generative
- Return type
array-like or float
Notes
The interpretation of x, p, and x_err is up to the fitfunc supplied during construction of this object (or the overridden model method of this object).
- property parameters¶
The refnx.analysis.Parameters set associated with the model.
- class refnx.analysis.Objective(model, data, lnsigma=None, use_weights=True, transform=None, logp_extra=None, name=None)[source]¶
Bases:
refnx.analysis.objective.BaseObjective
Objective function for using with curvefitters such as refnx.analysis.curvefitter.CurveFitter.
- Parameters
model (refnx.analysis.Model) – the generative model function. One can also provide an object that inherits refnx.analysis.Model.
data (refnx.dataset.Data1D) – data to be analysed.
lnsigma (float or refnx.analysis.Parameter, optional) –
Used if the experimental uncertainty (data.y_err) underestimated by a constant fractional amount. The experimental uncertainty is modified as:
s_n**2 = y_err**2 + exp(lnsigma * 2) * model**2
See Objective.logl for more details.
use_weights (bool) – use experimental uncertainty in calculation of residuals and logl, if available. If this is set to False, then you should also set self.lnsigma.vary = False, it will have no effect on the fit.
transform (callable, optional) – the model, data and data uncertainty are transformed by this function before calculating the likelihood/residuals. Has the signature transform(data.x, y, y_err=None), returning the tuple (transformed_y, transformed_y_err).
logp_extra (callable, optional) – user specifiable log-probability term. This contribution is in addition to the log-prior term of the model parameters, and model.logp, as well as the log-likelihood of the data. Has signature: logp_extra(model, data). The model will already possess updated parameters. Beware of including the same log-probability terms more than once.
name (str) – Name for the objective.
Notes
For parallelisation logp_extra needs to be picklable.
- chisqr(pvals=None)[source]¶
Calculates the chi-squared value for a given fitting system.
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
chisqr – Chi-squared value, np.sum(residuals**2).
- Return type
np.ndarray
- corner(**kwds)[source]¶
Corner plot of the chains belonging to the Parameters. Requires the corner and matplotlib packages.
- Parameters
kwds (dict) – passed directly to the corner.corner function
- Returns
fig
- Return type
matplotlib.Figure
object.
- covar(target='residuals')[source]¶
Estimates the covariance matrix of the Objective.
- Parameters
target ({"residuals", "nll", "nlpost"}) – Specifies what approach should be used to estimate covariance.
- Returns
covar – Covariance matrix
- Return type
np.ndarray
Notes
For most purposes the Jacobian of the ‘residuals’ should be used to calculate the covariance matrix, estimated as J.T x J. If an Objective cannot calculate residuals then the covariance matrix can be estimated by inverting a Hessian matrix created from either the ‘nll’ or ‘nlpost’ methods. The default ‘residuals’ approach falls back to ‘nll’ if a problem is experienced. The default ‘residuals’ setting is preferred as the other settings can sometimes experience instabilities during Hessian estimation with numerical differentiation.
- generative(pvals=None)[source]¶
Calculate the generative (dependent variable) function associated with the model.
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
model
- Return type
np.ndarray
- logl(pvals=None)[source]¶
Calculate the log-likelhood of the system
The major component of the log-likelhood probability is from the data. Extra potential terms are added on from the Model, self.model.logp, and the user specifiable logp_extra function.
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
logl – log-likelihood probability
- Return type
Notes
The log-likelihood is calculated as:
logl = -0.5 * np.sum(((y - model) / s_n)**2 + np.log(2 * pi * s_n**2)) logp += self.model.logp() logp += self.logp_extra(self.model, self.data)
where
s_n**2 = y_err**2 + exp(2 * lnsigma) * model**2
- logp(pvals=None)[source]¶
Calculate the log-prior of the system
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
logp – log-prior probability
- Return type
Notes
The log-prior is calculated as:
logp = np.sum(param.logp() for param in self.varying_parameters())
- logpost(pvals=None)[source]¶
Calculate the log-probability of the curvefitting system
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
logpost – log-probability
- Return type
Notes
The overall log-probability is the sum of the log-prior and log-likelihood. The log-likelihood is not calculated if the log-prior is impossible (logp == -np.inf).
- nll(pvals=None)[source]¶
Negative log-likelihood function
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
nll – negative log-likelihood
- Return type
- property npoints¶
int the number of points in the dataset.
- property parameters¶
refnx.analysis.Parameters
, all the Parameters contained in the fitting system.
- pgen(ngen=1000, nburn=0, nthin=1)[source]¶
Yield random parameter vectors from the MCMC samples. The objective state is not altered.
- Parameters
- Yields
pvec (np.ndarray) – A randomly chosen parameter vector
- plot(pvals=None, samples=0, parameter=None, fig=None)[source]¶
Plot the data/model.
Requires matplotlib be installed.
- Parameters
pvals (np.ndarray, optional) – Numeric values for the Parameter’s that are varying
samples (number) – If the objective has been sampled, how many samples you wish to plot on the graph.
parameter (refnx.analysis.Parameter) – Creates an interactive plot for the Parameter in Jupyter. Requires ipywidgets be installed. Use with %matplotlib notebook/qt.
fig (Figure instance, optional) – If fig is not supplied then a new figure is created. Otherwise the graph is created on the current axes on the supplied figure.
- Returns
fig, ax – matplotlib figure and axes objects.
- Return type
matplotlib.Figure
,matplotlib.Axes
- prior_transform(u)[source]¶
Calculate the prior transform of the system.
Transforms uniform random variates in the unit hypercube, u ~ uniform[0.0, 1.0), to the parameter space of interest, according to the priors on the varying parameters.
- Parameters
u (array-like) – Size of the varying parameters
- Returns
pvals – Scaled parameter values
- Return type
array-like
Notes
If a parameter has bounds, x ~ Unif[-10, 10) then the scaling from u to x is done as follows:
x = 2. * u - 1. # scale and shift to [-1., 1.) x *= 10. # scale to [-10., 10.)
- residuals(pvals=None)[source]¶
Calculates the residuals for a given fitting system.
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- Returns
residuals – Residuals, (data.y - model) / y_err.
- Return type
np.ndarray
- setp(pvals)[source]¶
Set the parameters from pvals.
- Parameters
pvals (array-like or refnx.analysis.Parameters) – values for the varying or entire set of parameters
- varying_parameters()[source]¶
- Returns
varying_parameters – The varying Parameter objects allowed to vary during the fit.
- Return type
- property weighted¶
bool Does the data have weights (data.y_err), and is the objective using them?
- class refnx.analysis.PDF(rv)[source]¶
Bases:
refnx.analysis.bounds.Bounds
A class that describes the probability distribution for a parameter.
- Parameters
rv (
scipy.stats.rv_continuous
or Object) – A continuous probability distribution. If rv is not an rv_continuous, then it must implement the logpdf and rvs methods.
Examples
>>> import scipy.stats as stats >>> from refnx.analysis import Parameter, PDF >>> p = Parameter(0.5) >>> # use a normal distribution for prior, mean=5 and sd=1. >>> p.bounds = PDF(stats.norm(5, 1)) >>> p.logp(), stats.norm.logpdf(0.5, 5, 1) (-11.043938533204672, -11.043938533204672)
- invcdf(q)[source]¶
Calculate the inverse of the cumulative distribution function for the uniform prior.
This is also known as the percent point function, or ppf.
- Parameters
q (array-like) – lower tail probability
- Returns
x – quantile corresponding to the lower tail probability q.
- Return type
array-like
- logp(val)[source]¶
Calculate the log-prior probability of a value with the probability distribution.
- class refnx.analysis.Parameter(value=0.0, name=None, bounds=None, vary=False, constraint=None)[source]¶
Bases:
refnx.analysis.parameter.BaseParameter
Class for specifying a variable.
- Parameters
value (float, optional) – Numerical Parameter value.
name (str, optional) – Name of the parameter.
bounds (refnx.analysis.Bounds, tuple, optional) – Sets the bounds for the parameter. Either supply a refnx.analysis.Bounds object (or one of its subclasses), or a (lower_bound, upper_bound) tuple.
vary (bool, optional) – Whether the Parameter is fixed during a fit.
constraint (expression, optional) – Python expression used to constrain the value during the fit.
- property constraint¶
- logp(pval=None)[source]¶
Calculate the log probability of the parameter
- Returns
prob – log probability of the parameter
- Return type
- setp(value=None, vary=None, bounds=None, constraint=None)[source]¶
Set several attributes of the parameter at once.
- Parameters
value (float, optional) – Numerical Parameter value.
vary (bool, optional) – Whether the Parameter is fixed during a fit.
bounds (refnx.analysis.Bounds, tuple, optional) – Sets the bounds for the parameter. Either supply a refnx.analysis.Bounds object (or one of its subclasses), or a (lower_bound, upper_bound) tuple.
constraint (expression, optional) – Python expression used to constrain the value during the fit.
- class refnx.analysis.Parameters(data=(), name=None)[source]¶
Bases:
collections.UserList
A sequence of Parameters
- Parameters
data (sequence) – A sequence of
Parameter
orParameters
name (str) – Name of this
Parameters
instance
- flattened(unique=False)[source]¶
A list of all the
Parameter
contained in this object, including those contained withinParameters
at any depth.
- logp()[source]¶
Calculates logp for all the parameters
- Returns
logp – Log probability for all the parameters
- Return type
- property nparam¶
- property parameters¶
- pgen(ngen=1000, nburn=0, nthin=1)[source]¶
Yield random parameter vectors from MCMC samples.
- Parameters
- Yields
pvec (np.ndarray) – A randomly chosen parameter vector
Notes
The entire parameter vector is yielded, not only the varying parameters. The reason for this is that some parameters may possess a chain if they are not varying, because they are controlled by a constraint.
- class refnx.analysis.Transform(form)[source]¶
Bases:
object
Mathematical transforms of numeric data.
- Parameters
One of:
- ’lin’
No transform is made
- ’logY’
log10 transform
- ’YX4’
YX**4 transform
- ’YX2’
YX**2 transform
- None
No transform is made
Notes
You ask for a transform to be carried out by calling the Transform object directly.
>>> x = np.linspace(0.01, 0.1, 11) >>> y = np.linspace(100, 1000, 11) >>> y_err = np.sqrt(y) >>> t = Transform('logY') >>> ty, te = t(x, y, y_err) >>> ty array([2. , 2.2787536 , 2.44715803, 2.56820172, 2.66275783, 2.74036269, 2.80617997, 2.86332286, 2.91381385, 2.95904139, 3. ])
- refnx.analysis.autocorrelation_chain(chain, nburn=0, nthin=1)[source]¶
Calculate the autocorrelation function
- Parameters
chain (np.ndarray) – The MCMC chain - (nsteps, nwalkers, ndim) or (nsteps, ntemps, nwalkers, ndim)
- Returns
acfs – The autocorrelation function, acfs.shape=(lags, nvary)
- Return type
np.ndarray
- refnx.analysis.integrated_time(x, c=5, tol=50, quiet=False)[source]¶
Estimate the integrated autocorrelation time of a time series.
This estimate uses the iterative procedure described on page 16 of Sokal’s notes to determine a reasonable window size.
- Parameters
x – The time series. If multidimensional, set the time axis using the
axis
keyword argument and the function will be computed for every other axis.c (Optional[float]) – The step size for the window search. (default:
5
)tol (Optional[float]) – The minimum number of autocorrelation times needed to trust the estimate. (default:
50
)quiet (Optional[bool]) – This argument controls the behavior when the chain is too short. If
True
, give a warning instead of raising anAutocorrError
. (default:False
)
- Returns
- An estimate of the integrated autocorrelation time of
the time series
x
computed along the axisaxis
.
- Return type
float or array
- Raises
- AutocorrError: If the autocorrelation time can’t be reliably estimated
from the chain and
quiet
isFalse
. This normally means that the chain is too short.
- refnx.analysis.load_chain(f)[source]¶
Loads a chain from disk. Does not change the state of a CurveFitter object.
- Parameters
f (str or file-like) – File containing the chain.
- Returns
chain – The loaded chain - (nsteps, nwalkers, ndim) or (nsteps, ntemps, nwalkers, ndim)
- Return type
array
- refnx.analysis.possibly_create_parameter(value, name='', bounds=None, vary=False, constraint=None)[source]¶
If supplied with a Parameter return it. If supplied with float, wrap it in a Parameter instance.
- Parameters
value (float, optional) – Numerical Parameter value.
name (str, optional) – Name of the parameter.
bounds (refnx.analysis.Bounds, tuple, optional) – Sets the bounds for the parameter. Either supply a refnx.analysis.Bounds object (or one of its subclasses), or a (lower_bound, upper_bound) tuple.
vary (bool, optional) – Whether the Parameter is fixed during a fit.
constraint (expression, optional) – Python expression used to constrain the value during the fit.
- Returns
parameter
- Return type
- refnx.analysis.process_chain(objective, chain, nburn=0, nthin=1, flatchain=False)[source]¶
Process the chain produced by a sampler for a given Objective
- Parameters
objective (refnx.analysis.Objective) – The Objective function that the Posterior was sampled for
chain (array) – The MCMC chain
nburn (int, optional) – discard this many steps from the start of the chain
nthin (int, optional) – only accept every nthin samples from the chain
flatchain (bool, optional) – collapse the walkers down into a single dimension.
- Returns
[(param, stderr, chain)] – List of (param, stderr, chain) tuples. If isinstance(objective.parameters, Parameters) then param is a Parameter instance. param.value, param.stderr and param.chain will contain the median, stderr and chain samples, respectively. Otherwise param will be a float representing the median of the chain samples. stderr is the half width of the [15.87, 84.13] spread (similar to standard deviation) and chain is an array containing the MCMC samples for that parameter.
- Return type
Notes
The chain should have the shape (iterations, nwalkers, nvary) or (iterations, ntemps, nwalkers, nvary) if parallel tempering was employed. The burned and thinned chain is created via: chain[nburn::nthin]. Note, if parallel tempering is employed, then only the lowest temperature of the parallel tempering chain is processed and returned as it corresponds to the (lowest energy) target distribution. If flatten is True then the burned/thinned chain is reshaped and arr.reshape(-1, nvary) is returned. This function has the effect of setting the parameter stderr’s.
- refnx.analysis.pymc3_model(objective)[source]¶
Creates a pymc3 model from an Objective.
Requires theano and pymc3 be installed. This is an experimental feature.
- Parameters
objective (refnx.analysis.Objective) –
- Returns
model
- Return type
pymc3.Model
Notes
The varying parameters are renamed ‘p0’, ‘p1’, etc, as it’s vital in pymc3 that all parameters have their own unique name.