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@roban
Created Jan 24, 2011
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Routines related to plotting 2D distributions of parameters (mainly for pymc models).
"""Routines related to plotting 2D distributions of parameters.
The core of this module is plot2Ddist, which plots a two-dimensional
distribution with 1D marginal histograms along each axis and optional
features like contours and lines indicating ranges and true values.
"""
import itertools
import math
import copy
import pylab
import numpy
import pymc
import matplotlib.patches
from mpl_toolkits.axes_grid1 import make_axes_locatable
import scipy.stats
def applyFuncToTrace(function, variables, container=None, chain=-1,
trim=0, thin=1):
"""Apply function to the trace values of variables.
`variables` is a list of N arrays, pymc traces, or pymc objects with
corresponding traces in `container.db`.
`function` is a function that takes N arguments.
`container` is an optional pymc model with a `db` attribute
containing the traces of each variable.
`chain` specifies the chain to use (only used if `container` is
specified).
"""
traces = vars_to_trace(variables, container, chain=chain)
arrays =[trace[trim::thin] for trace in traces]
return function(*arrays)
def fakeDeterministicFromFunction(function, variables, container=None, chain=-1,
trim=0, thin=1,
**detargs):
"""Create a Deterministic object with a trace calculated from
applying `function` to the traces of `variables`.
"""
tracevalue = applyFuncToTrace(function, variables, container, chain, trim, thin)
return fakeDeterministicFromValue(tracevalue.transpose(), **detargs)
def func_envelopesFromFunction(function, variables,
xlims, npoints=100,
container=None, chain=-1, trim=0, thin=1,
display=True,
alpha=0.5, new=True, **detargs):
"""
"""
x = numpy.linspace(xlims[0], xlims[1], npoints).reshape(npoints,1)
def newfunction(*vals):
return function(x, *vals)
det = fakeDeterministicFromFunction(newfunction, variables,
container, chain, trim, thin, **detargs)
envs = pymc.Matplot.func_envelopes(det)
if display:
for env in envs:
env.display(x.flatten(), alpha=alpha, new=new)
new = False
return x.flatten(), envs
def fakeDeterministicFromValue(tracevalue,
eval=None, doc="", name="", parents={}):
"""Create a Deterministic object which will return tracevalue when
it's trace method is called.
"""
if eval is None:
eval = lambda : None
v = pymc.Deterministic(eval, doc, name, parents)
v.trace = lambda : tracevalue
return v
def createDeterministicTrace(mcmodel, deterministic,
chain=-1, chain_length=None):
"""Create a trace for a Deterministic variable.
Steps through the trace history of mcmodel, calculating the value
of the deterministic variable for each iteration and returning the
results.
Notes
-----
This does not actually create or store a trace object, it
just returns an array of values correpsonding to the traces of the
parent variables.
This can be fairly slow. See applyFuncToTrace, which opperates on
trace arrays and may therefore be much faster, though less
convenient in some cases.
"""
if chain_length is None:
chain_length = mcmodel._cur_trace_index
values = []
for i in xrange(chain_length):
print "%i of %i" % (i, chain_length)
mcmodel.remember(chain=chain, trace_index=i)
values.append(deterministic.get_value())
values = numpy.asarray(values)
return values
def plot_AM_correlation(mcmodel, startvariances=None, variables=None,
trim=0, thin=1, plotcov=True, plotcorrelation=True,
plotvalues=True, plotdeviance=False):
"""Plot correlation or covariance from AdaptativeMetropolis traces.
mcmodel -- a pymc MCMC object with a db containing an
AdaptativeMetropolis trace.
"""
oldnumpyerrsettings = numpy.seterr(invalid='ignore')
cname = None
for key in mcmodel.db.trace_names[-1]:
if key.startswith('AdaptiveMetropolis'):
cname = key
#print cname
if cname is None:
print "Could not find an AdaptiveMetropolis trace."
return
Ctrace = mcmodel.db.trace(cname)[trim::thin]
indices = numpy.arange(trim, len(mcmodel.db.trace(cname)[:]), thin)
### Figure out order of stochastics. ###
positions = []
stochlist = list(mcmodel.stochastics.copy())
icount = 0
olength = len(stochlist)
cname = cname.replace('AdaptiveMetropolis','')
while len(stochlist) > 0:
icount += 1
stoch = stochlist.pop()
print stoch
if cname.count(stoch.__name__) == 0:
print "Couldn't find %s in %s" % (stoch.__name__, cname)
continue
positions.append([stoch, cname.find('_' + stoch.__name__)])
# Sort list by position in cname string.
positions.sort(key=lambda l: l[1])
stochlist = [l[0] for l in positions]
names = [s.__name__ for s in stochlist]
title = " ".join(names)
print title
covlist = []
fig1 = pylab.figure()
fig1.subplots_adjust(right=0.7)
fig1.set_label('AMcorrelations')
ax1 = pylab.gca()
divider = make_axes_locatable(ax1)
if plotvalues:
ax2 = divider.append_axes("bottom", 1.5, pad=0.0, sharex=ax1)
fig1.sca(ax1)
if plotdeviance:
ax3 = divider.append_axes("top", 1.5, pad=0.0, sharex=ax1)
fig1.sca(ax1)
pylab.title(cname)
plottedinds = set([])
inds = set(range(Ctrace.shape[1]))
colors = ['r','g','b','c','m','k','y']
for (i, stoch) in enumerate(stochlist):
if variables is not None:
if stoch not in variables:
continue
plottedinds.add(i)
if plotvalues:
ax2.plot(indices, mcmodel.db.trace(stoch.__name__)[trim::thin])
if plotdeviance:
ax3.plot(indices, mcmodel.db.trace('deviance')[trim::thin])
if not plotcorrelation:
lines = pylab.plot(indices, Ctrace[:,i,i]**0.5, alpha='0.5',
lw=3.0, label=names[i] + " stdev",
color=colors[i])
if startvariances is not None:
pylab.axhline(y=startvariances[stoch]**0.5, ls='-',
c=lines[0]._color, lw=1.5)
else:
lines = pylab.plot(indices, (Ctrace[:,i,i]/Ctrace[-1,i,i])**0.5,
alpha='0.5',
lw=3.0, label=names[i] + " stdev/stdev_final",
color=colors[i])
if startvariances is not None:
pylab.axhline(y=(startvariances[stoch]/Ctrace[-1,i,i])**0.5,
ls='-',
c=colors[i], lw=1.5)
if not plotcov:
continue
for j in inds.difference(plottedinds):
if plotcorrelation:
cov = Ctrace[:,i,j]/(Ctrace[:,i,i]**0.5 * Ctrace[:,j,j]**0.5)
mag = abs(cov)
else:
cov = Ctrace[:,i,j]
mag = abs(cov)**0.5
sign = (cov > 0) * 1 + (cov<=0)*-1
covlist.append([names[i]+' * '+names[j], mag[-1], sign[-1]])
pylab.plot(indices, sign*mag, alpha='0.9',
lw=3.0, c=colors[i], ls='--')
pylab.plot(indices, -sign*mag, alpha='0.9',
lw=3.0, c=colors[i], ls=':')
pylab.plot(indices, mag, alpha='0.9',
lw=1.0, color=colors[j], ls='-',
label=names[i]+' * '+names[j])
covlist.sort(key=lambda l: l[1], reverse=True)
for l in covlist:
print "%50s: %.3g" % (l[0], l[1]*l[2])
#pylab.legend(loc='upper left', bbox_to_anchor=(1.00,1.0,0.25,-1.0))
pylab.legend(loc=(1.0,0.0))
if plotcorrelation:
pylab.ylim(ymin=0)
else:
pylab.yscale('log')
pylab.draw()
numpy.seterr(**oldnumpyerrsettings)
def frac_inside_poly(x,y,polyxy):
"""Calculate the fraction of points x,y inside polygon polyxy.
polyxy -- list of x,y coordinates of vertices.
"""
xy = numpy.vstack([x,y]).transpose()
return float(sum(matplotlib.nxutils.points_inside_poly(xy, polyxy)))/len(x)
def fracs_inside_contours(x, y, contours):
"""Calculate the fraction of points x,y inside each contour level.
contours -- a matplotlib.contour.QuadContourSet
"""
fracs = []
for (icollection, collection) in enumerate(contours.collections):
path = collection.get_paths()
if len(path) == 0:
print "No paths found for contour."
frac = 0
else:
path = path[0]
pathxy = path.vertices
frac = frac_inside_poly(x,y,pathxy)
fracs.append(frac)
return fracs
def frac_label_contours(x, y, contours, format='%.3f'):
"""Label contours according to the fraction of points x,y inside.
"""
fracs = fracs_inside_contours(x,y,contours)
levels = contours.levels
labels = {}
for (level, frac) in zip(levels, fracs):
labels[level] = format % frac
contours.clabel(fmt=labels)
def contour_enclosing(x, y, fractions, xgrid, ygrid, zvals,
axes, nstart = 200,
*args, **kwargs):
"""Plot contours encompassing specified fractions of points x,y.
"""
# Generate a large set of contours initially.
contours = axes.contour(xgrid, ygrid, zvals, nstart,
extend='both')
# Set up fracs and levs for interpolation.
levs = contours.levels
fracs = numpy.array(fracs_inside_contours(x,y,contours))
sortinds = numpy.argsort(fracs)
levs = levs[sortinds]
fracs = fracs[sortinds]
# Find the levels that give the specified fractions.
levels = scipy.interp(fractions, fracs, levs)
# Remove the old contours from the graph.
for coll in contours.collections:
coll.remove()
# Reset the contours
contours.__init__(axes, xgrid, ygrid, zvals, levels, *args, **kwargs)
return contours
def obj_to_names(variables):
"""Return a list of names for the given list of objects.
Works for any object with a __name__ attribute.
"""
names = []
for var in variables:
names.append(var.__name__)
return names
def names_to_obj(names, container):
"""Return a list of attributes given attribute names and container
object.
"""
variables = []
for name in names:
variables.append(getattr(container,name))
return variables
def names_to_trace(names, container, chain=-1):
"""Return a list of traces given variable names and pymc object.
Accesses the traces using 'container.trace(name, chain=chain)'.
"""
traces = []
for name in names:
traces.append(container.trace(name, chain=chain))
return traces
def names_to_traceValDict(names, container, chain=-1,
trim=0, thin=1, transpose=False):
"""Return a dict of trace values given variable names and pymc object.
Accesses the traces using 'container.trace(name, chain=chain)'.
"""
traces = {}
for name in names:
t = container.trace(name, chain=chain)[trim::thin]
if transpose:
t = t.reshape((len(t),1))
traces[name] = t
return traces
def vars_to_trace(variables, container=None, chain=-1):
"""Return a list of traces given variables and a pymc model.
If container is specified, retrieve traces from
container.db.trace(varname).
See also: obj_to_names, names_to_trace
"""
names = obj_to_names(variables)
if container:
return names_to_trace(names, container, chain=chain)
else:
return [var.trace(chain=chain) for var in variables]
def plot2DdistsAllPairs(variables, labels=None, mcmodel=None, axeslists=None,
*args, **kwargs):
"""Run plot2Ddist on all pairs in the set `variables`.
"""
pairs = itertools.combinations(variables, 2)
length = int(math.factorial(len(variables))
/ (2. * math.factorial(len(variables) - 2)))
if labels is None:
pairlabels = itertools.cycle([None])
else:
pairlabels = itertools.combinations(labels, 2)
if axeslists is None:
axeslists = [None] * length
for (i, (pair, pairlabel, axeslist)) in enumerate(zip(pairs,
pairlabels,
axeslists)):
if mcmodel is None:
traces = pair
else:
names = obj_to_names(pair)
traces = names_to_trace(names, mcmodel)
if pairlabel is None:
pairlabel = names
results = plot2Ddist(traces, labels=pairlabel, axeslist=axeslist,
*args, **kwargs)
axeslists[i] = results['axeslist']
return axeslists
def plot2DdistsPairs(xvar, yvars, *args, **kwargs):
"""Run plot2Ddist on all xvar paired with all other `yvars`.
"""
for yvar in yvars:
plot2Ddist([xvar, yvar], *args, **kwargs)
def plot2Ddist(variables, axeslist=None, truevalues=None, markvalues=None,
limitvalues=None, mcmodel=None, chain=-1,
trim=0, thin=1, histbinslist=[100, 100],
labels=None, scaleview=True, label=None,
plotscatter=True, plothists=True, plotcontours=False,
contourKDEthin=None, contourNGrid=100,
contourFractions=[0.6827, 0.9545, 0.9973],
contourKDECovFactor=None,
labelcontours=True,
calcp=False, plot_truevalue_contour=True,
xscale='linear', yscale='linear',
scatterstyle={}, histstyle={}, contourstyle={}, **styleArgs):
"""Plot joint distribution of two variables, with marginal histograms.
The resulting graphic includes (at your discretion):
* a scatter plot of the 2D distribution of the two variables
* estimated credible regions for the distribution
* marginal histograms for each variable
See plot2Ddist_example.py for an example:
> plot2Ddist([a, b], truevalues=[intercept, slope], **styleargs)
Notes
-----
The contour plotting can be quite slow for large samples because
of the gaussian kernel density estimation. Try passing a larger
value for contourKDEthin to speed it up.
Contouring code inspired by Abraham Flaxman's
http://gist.github.com/626689
Returns
-------
results -- a dictionary of results, which may contain the following
'axeslist' -- a list of three Matplotlib Axes for: the joint
plot, marginal x histogram, and marginal y histogram,
respectively.
'contours' -- the Matplotlib contours (if plotcontours)
'gkde' -- the scipy.stats.gaussian_kde object (if plotcontours)
'truevalue_p' -- the fraction of points inside the KDE contour
on which truevalue falls (if calcp)
Inputs
------
variables -- list-like of length 2
a list of two array-like or pymc.Variable objects. The lengths
of the arrays or variable traces should be equal.
axeslist -- list-like of length 3
a list of three Matplotlib Axes for: the joint plot, marginal
x histogram, and marginal y histogram, respectively.
truevalues -- list-like of length 2
a list of the true values for each variable
trim -- int
plot elements starting at index trim (can be negative)
thin -- int
plot only every thin-th element of each variable
histbinlist -- list-like of length 2
specify the bins (number or limits) for x and y marginal histograms.
labels -- list-like of two strings
the x and y axis labels
scaleview -- bool
whether to set the axes limits according to the plotted data
plotscatter, plothists, plotcontours -- bool
whether to plot the scatter, marginal histograms, and contours
scatterstyle, histstyle, contourstyle -- dict-like
additional keyword arguments for the plot, hist, or contour commands
contourKDEthin -- int
factor by which to thin the samples before calculating the
gaussian kernel density estimate for contouring
contourNGrid -- int
size of the grid to use (in each dimension) for the contour plotting
contourFractions -- list-like
countours are chosen to include the fractions of points specified here
labelcontours -- bool
whether to label the contours with the fraction of points enclosed
styleArgs --
leftover arguments are passed to both the plot and hist commands
"""
results = {}
# Determine labels
if labels is None:
passedlabels = False
labels = [None, None]
else:
passedlabels = True
variables = list(variables)
if mcmodel is not None:
if not passedlabels:
labels = obj_to_names(variables)
variables = vars_to_trace(variables, mcmodel, chain=chain)
else:
for (ivar, variable) in enumerate(variables):
# Get the trace if this is a pymc.Variable object.
if isinstance(variable, pymc.Variable):
variables[ivar] = variable.trace()
if hasattr(variable, '__name__') and not passedlabels:
labels[ivar] = variable.__name__
if isinstance(truevalues, dict):
tv = (truevalues.get(labels[0], None),
truevalues.get(labels[1], None))
truevalues = tv
if isinstance(limitvalues, dict):
lims = (limitvalues.get(labels[0], None),
limitvalues.get(labels[1], None))
limitvalues = lims
if isinstance(markvalues, dict):
mv = (markvalues[variables[0].__name__],
markvalues[variables[1].__name__])
markvalues = mv
### Set up figures and axes. ###
if axeslist is None:
fig1 = pylab.figure(figsize=(6,6))
ax1 = pylab.gca()
fig1.set_label('traces')
divider = make_axes_locatable(ax1)
ax2 = divider.append_axes("top", 1.5, pad=0.0, sharex=ax1)
ax3 = divider.append_axes("right", 1.5, pad=0.0, sharey=ax1)
ax1.set_xscale(xscale)
ax2.set_xscale(xscale)
ax1.set_yscale(yscale)
ax3.set_yscale(yscale)
for tl in (ax2.get_xticklabels() + ax2.get_yticklabels() +
ax3.get_xticklabels() + ax3.get_yticklabels()):
tl.set_visible(False)
axeslist = (ax1, ax2, ax3)
else:
ax1, ax2, ax3 = axeslist
results['axeslist'] = axeslist
if label is not None:
ax1.get_figure().set_label('traces' + label)
# Thin and trim variables.
trim = int(trim)
x = numpy.ravel(variables[0][trim::thin])
y = numpy.ravel(variables[1][trim::thin])
### Plot the variables. ###
# Plot 2D scatter of variables.
if plotscatter:
style = {'marker':'o', 'color':'r', 'alpha':0.5}
style.update(styleArgs)
style.update(scatterstyle)
ax1.scatter(x, y, **style)
if plotcontours or calcp:
if contourKDEthin is None:
contourKDEthin=1 + int(len(x)*(1.-max(contourFractions))/60)
print "Using countourKDEthin = %i" % (contourKDEthin)
xkde = numpy.ravel(variables[0][trim::contourKDEthin])
ykde = numpy.ravel(variables[1][trim::contourKDEthin])
style = {'linewidths':2.0, 'alpha':0.75, 'colors':'k',
#'cmap':matplotlib.cm.Greys,
'zorder':10}
style.update(styleArgs)
style.update(contourstyle)
if 'color' in style:
style['colors'] = style['color']
gkde = scipy.stats.gaussian_kde([xkde,ykde])
if contourKDECovFactor is not None:
gkde.covariance_factor = lambda:contourKDECovFactor
gkde._compute_covariance()
results['gkde'] = gkde
spans = 0.75 * numpy.array([max(x)-min(x), max(y)-min(y)])
mids = 0.5 * numpy.array([max(x)+min(x), max(y)+min(y)])
xgrid, ygrid = \
numpy.mgrid[mids[0]-spans[0]:mids[0]+spans[0]:contourNGrid * 1j,
mids[1]-spans[1]:mids[1]+spans[1]:contourNGrid * 1j]
zvals = numpy.array(gkde.evaluate([xgrid.flatten(),
ygrid.flatten()])
).reshape(xgrid.shape)
if plotcontours:
contours = contour_enclosing(x, y, contourFractions,
xgrid, ygrid, zvals,
ax1, **style)
results['contours'] = contours
if calcp and truevalues is not None:
truevalue_pdensity = gkde.evaluate([truevalues[0],
truevalues[1]])[0]
style.update({'linewidths':1.0,
'linestyles':'dashed'
})
truevalue_contour = ax1.contour(xgrid, ygrid, zvals,
[truevalue_pdensity], **style)
results['truevalue_p'] = fracs_inside_contours(x, y,
truevalue_contour)[0]
if not plot_truevalue_contour:
truevalue_contour.collections[0].remove()
# Plot marginal histograms.
histbinslist = copy.copy(histbinslist)
if plothists:
if numpy.isscalar(histbinslist[0]):
nbins = histbinslist[0]
x_range = [numpy.min(x), numpy.max(x)]
if xscale is 'linear':
histbinslist[0] = numpy.linspace(x_range[0], x_range[1], nbins)
if xscale is 'log':
histbinslist[0] = numpy.logspace(numpy.log10(x_range[0]),
numpy.log10(x_range[1]), nbins)
if numpy.isscalar(histbinslist[1]):
nbins = histbinslist[1]
y_range = [numpy.min(y), numpy.max(y)]
if yscale is 'linear':
histbinslist[1] = numpy.linspace(y_range[0], y_range[1], nbins)
if yscale is 'log':
histbinslist[1] = numpy.logspace(numpy.log10(y_range[0]),
numpy.log10(y_range[1]), nbins)
style = {'histtype':'step', 'normed':True, 'color':'k'}
style.update(styleArgs)
style.update(histstyle)
ax2.hist(x, histbinslist[0], **style)
ax3.hist(y, histbinslist[1], orientation='horizontal', **style)
# Set the limits of the axes.
if scaleview:
ax1.set_xmargin(0.05)
ax1.set_ymargin(0.05)
ax1.relim()
ax2.relim()
ax3.relim()
ax2.autoscale_view(tight=True)
ax3.autoscale_view(tight=True)
ax1.autoscale_view(tight=True)
ax1.autoscale(False)
ax2.autoscale(False)
ax3.autoscale(False)
ax2.set_ylim(bottom=0)
ax3.set_xlim(left=0)
# Plot lines for the true values.
if truevalues is not None:
if truevalues[0] is not None:
ax1.axvline(x=truevalues[0], ls=':', c='k')
ax2.axvline(x=truevalues[0], ls=':', c='k')
if truevalues[1] is not None:
ax1.axhline(y=truevalues[1], ls=':', c='k')
ax3.axhline(y=truevalues[1], ls=':', c='k')
if limitvalues is not None:
if limitvalues[0] is not None:
ax1.axvline(x=limitvalues[0][0], ls=':', c='b')
ax1.axvline(x=limitvalues[0][1], ls=':', c='b')
ax2.axvline(x=limitvalues[0][0], ls=':', c='b')
ax2.axvline(x=limitvalues[0][1], ls=':', c='b')
if limitvalues[1] is not None:
ax1.axhline(y=limitvalues[1][0], ls=':', c='b')
ax1.axhline(y=limitvalues[1][1], ls=':', c='b')
ax3.axhline(y=limitvalues[1][0], ls=':', c='b')
ax3.axhline(y=limitvalues[1][1], ls=':', c='b')
if markvalues is not None:
style = dict(marker='o', markersize=10, color='r', alpha=0.75)
style.update(styleArgs)
ax1.plot([markvalues[0]], [markvalues[1]], **style)
if labels[0] is not None:
ax1.set_xlabel(labels[0])
if labels[1] is not None:
ax1.set_ylabel(labels[1])
if plotcontours and labelcontours:
frac_label_contours(x, y, contours)
return results
def plot_tcorr_windows(variable, nwindows=7, label=None, axes=None,
thin=1, trim=0, **args):
"""Plot the autocorrelation of a trace divided into windows.
The trace is split into nwindows segements, and the
autocorrelation of each segment is plotted.
"""
if hasattr(variable, '__name__') and label is None:
label = variable.__name__
print "the label is ", label
if isinstance(variable, pymc.Variable):
variable = variable.trace().flatten()
if label is None:
label = ''
x = variable[trim::thin]
windowlen = len(x)/nwindows
windows = numpy.arange(nwindows+1) * windowlen
if windows[-1] > len(x):
windows[-1] = len(x)
for iw in range(nwindows):
newlabel = label + ' %i:%i' % (windows[iw],windows[iw+1])
axes = plot_trace_correlation(x[windows[iw]:windows[iw+1]],
label=newlabel, axes=axes, **args)
axes.legend()
pylab.draw()
return axes
def plot_trace_correlation(variable, thin=1, trim=0, label=None, axes=None,
maxlags=50, **styleArgs):
"""Plot the autocorrelation of a sample.
Inspired by Abraham Flaxman's http://gist.github.com/626689
"""
if axes is None:
fig = pylab.figure()
fig.set_label('acorr')
axes = pylab.gca()
if hasattr(variable, '__name__') and label is None:
label = variable.__name__
if isinstance(variable, pymc.Variable):
variable = variable.trace()
x = variable[trim::thin]
if maxlags >= len(x):
maxlags = len(x) - 1
style = {'usevlines':False, 'ls':'-', 'marker':'.', 'label':label}
style.update(styleArgs)
axes.acorr(x, detrend=matplotlib.mlab.detrend_mean, maxlags=maxlags,
**style)
axes.axhline(0)
#axes.set_ylim([-0.1,1.1])
#axes.set_yticks([0,.5,1.])
axes.set_xlabel('offset')
axes.set_ylabel('auto correlation')
pylab.draw()
return axes
"""An example of plot2Ddist.
Originally based on an example by Anand Patil:
http://groups.google.com/group/pymc/browse_thread/thread/afe91c4d9440d6da
"""
import pymc as pm
import numpy as np
import matplotlib.pyplot as pl
# Set up parameters. Our model is y = a + b x + c x^2
a = pm.Uninformative('a',0)
b = pm.Uninformative('b',0)
c = pm.Uninformative('c',0)
v = pm.OneOverX('v',1)
# Locations of observations.
nx = 50
span = 5.0
x = np.linspace(-span/2,span/2,nx)
# Generate mock set of data.
slope = 2.0
intercept = 1.0
curve = 3.0
sigma = 3.0
data = (x**2)*curve + x*slope + intercept + np.random.normal(size=len(x))*sigma
# Observed variable.
y = pm.Normal('y', a+b*x+c*x**2, 1./v,value=data,observed=True)
ypred = pm.Normal('ypred',a+b*x+c*x**2,1./v)
# Set up MCMC chain.
M = pm.MCMC([a,b,c,v,y,ypred])
M.use_step_method(pm.AdaptiveMetropolis, [a,b,c,v], tally=True)
# Sample.
M.isample(20000,5000,10)
# Plot the function and envelope.
pl.figure()
env = pm.Matplot.func_envelopes(ypred)
for e in env:
e.display(x,.5,new=False)
pl.plot(x,data,'r.',markersize=4)
pl.plot(x,data,'r.',markersize=4)
# Plot the parameter distribution from the samples.
import plot2Ddist
scatterstyle={'color':'r', 'alpha':0.1}
styleargs = {'color':'k', 'scatterstyle':scatterstyle}
truevalues = dict(b = slope,
a = intercept,
c = curve,
v = sigma**2.)
#plot2Ddist.plot2DdistsAllPairs([a,b,c,v], truevalues=truevalues,
# **styleargs)
plot2Ddist.plot2DdistsPairs(a, [b,c,v], truevalues=truevalues,
**styleargs)
#plot2Ddist.plot_AM_correlation(M)
plot2Ddist.plot_AM_correlation(M, variables=[a,v])
pl.show()
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