5 2 - Introduction PyMC3.

# Importing GemPy
import gempy as gp

# Importing auxiliary libraries
import os
import numpy as np
import matplotlib.pyplot as plt
import pymc3 as pm
import arviz as az

from gempy.bayesian import plot_posterior as pp
from importlib import reload
from matplotlib.ticker import StrMethodFormatter

Model definition

This is to make it work in sphinx gallery

cwd = os.getcwd()
if not 'examples' in cwd:
    path_dir = os.getcwd()+'/examples/tutorials/ch5_probabilistic_modeling'
else:
    path_dir = cwd

geo_model = gp.load_model(r'/2-layers', path=path_dir+'/2-layers', recompile=True)

Out:

Active grids: ['regular']
Active grids: ['regular' 'topography']
Setting kriging parameters to their default values.
Compiling theano function...
Level of Optimization:  fast_compile
Device:  cpu
Precision:  float64
Number of faults:  0
Compilation Done!
Kriging values:
                   values
range            1.3e+04
$C_o$            4.2e+06
drift equations      [3]

geo_model.modify_surface_points(2, Z=1000)
gp.compute_model(geo_model)

Out:

Lithology ids
  [3. 3. 3. ... 1. 1. 1.]

def plot_geo_setting_well():
    device_loc = np.array([[6e3, 0, 3700]])
    p2d = gp.plot_2d(geo_model, show_topography=True, legend=False)

    well_1 = 3.41e3
    well_2 = 3.6e3
    p2d.axes[0].scatter([3e3], [well_1], marker='^', s=400, c='#71a4b3', zorder=10)
    p2d.axes[0].scatter([9e3], [well_2], marker='^', s=400, c='#71a4b3', zorder=10)
    p2d.axes[0].scatter(device_loc[:, 0], device_loc[:, 2], marker='x', s=400, c='#DA8886', zorder=10)

    p2d.axes[0].vlines(3e3, .5e3, well_1, linewidth=4, color='gray')
    p2d.axes[0].vlines(9e3, .5e3, well_2, linewidth=4, color='gray')
    p2d.axes[0].vlines(3e3, .5e3, well_1)
    p2d.axes[0].vlines(9e3, .5e3, well_2)
    p2d.axes[0].set_xlim(2900, 3100)
    plt.savefig('well.svg')
    plt.show()

plot_geo_setting_well()

# Thickness measurements
# ----------------------

y_obs = [2.12]
y_obs_list = [2.12, 2.06, 2.08, 2.05, 2.08, 2.09,
              2.19, 2.07, 2.16, 2.11, 2.13, 1.92]
np.random.seed(4003)

Normal-several points

with pm.Model() as model:
    mu = pm.Normal('$\mu$', 2.08, .07)
    sigma = pm.Gamma('$\sigma$', 0.3, 3)
    y = pm.Normal('$y$', mu, sigma, observed=y_obs_list)

mu

Out:

$\mu$

sigma

Out:

$\sigma$

y

Out:

$y$

Sampling

with model:
    prior = pm.sample_prior_predictive(1000)
    trace = pm.sample(1000, discard_tuned_samples=False, cores=1)
    post = pm.sample_posterior_predictive(trace)

Out:

Auto-assigning NUTS sampler...
Initializing NUTS using jitter+adapt_diag...
Sequential sampling (2 chains in 1 job)
NUTS: [$\sigma$, $\mu$]
█
█
Sampling 2 chains for 1_000 tune and 1_000 draw iterations (2_000 + 2_000 draws total) took 3 seconds.
█

data = az.from_pymc3(trace=trace,
                     prior=prior,
                     posterior_predictive=post)

Out:

arviz.data.io_pymc3 - WARNING - posterior predictive variable $y$'s shape not compatible with number of chains and draws. This can mean that some draws or even whole chains are not represented.

az.plot_trace(data)
plt.show()

reload(pp)
p = pp.PlotPosterior(data)
p.create_figure(figsize=(9, 3), joyplot=False, marginal=False)
p.plot_normal_likelihood('$\mu$', '$\sigma$', '$y$', iteration=-1, hide_bell=True)
p.likelihood_axes.set_xlim(1.90, 2.2)
p.likelihood_axes.xaxis.set_major_formatter(StrMethodFormatter('{x:,.2f}'))
for tick in p.likelihood_axes.get_xticklabels():
    tick.set_rotation(45)
plt.show()

reload(pp)
p = pp.PlotPosterior(data)
p.create_figure(figsize=(9, 3), joyplot=False, marginal=False)
p.plot_normal_likelihood('$\mu$', '$\sigma$', '$y$', iteration=-1, hide_lines=True)
p.likelihood_axes.set_xlim(1.70, 2.40)
p.likelihood_axes.xaxis.set_major_formatter(StrMethodFormatter('{x:,.2f}'))
for tick in p.likelihood_axes.get_xticklabels():
    tick.set_rotation(45)
plt.show()

Joyplot

%matplotlib inline

reload(pp)
p = pp.PlotPosterior(data)

p.create_figure(figsize=(9, 9), joyplot=True, marginal=False, likelihood=False, n_samples=31)
p.plot_joy(('$\mu$', '$\sigma$'), '$y$', iteration=14)
plt.show()

Join probability

sphinx_gallery_thumbnail_number = 6

reload(pp)
p = pp.PlotPosterior(data)

p.create_figure(figsize=(9, 5), joyplot=False, marginal=True, likelihood=True)
p.plot_marginal(var_names=['$\mu$', '$\sigma$'],
                plot_trace=False, credible_interval=.93, kind='kde')

p.plot_normal_likelihood('$\mu$', '$\sigma$', '$y$', iteration=-1, hide_lines=True)
p.likelihood_axes.set_xlim(1.70, 2.40)
plt.show()

Full plot

reload(pp)
p = pp.PlotPosterior(data)

p.create_figure(figsize=(9, 5), joyplot=True, marginal=True, likelihood=True, n_samples=11)

p.plot_posterior(['$\mu$', '$\sigma$'], ['$\mu$', '$\sigma$'], '$y$',
                 marginal_kwargs={'plot_trace': False, 'credible_interval': .93, 'kind': 'kde'})
plt.show()