Getting Started

The easiest way to get started with MATK is to open an ipython/python terminal and copy and paste the example code below into your terminal. After that, the Examples section can be explored for additional ideas of how MATK can facilitate your model analysis.

Load MATK module

Start by importing the MATK module:

import matk

We’ll use numpy and some scipy functions also, so load those modules:

import numpy
from scipy import arange, randn, exp

Define Model

To perform a model analysis, MATK needs a model in the form of a python function that accepts a dictionary of parameter values keyed by parameter names as the first argument and returns an integer, float, array, or dictionary of model results keyed by result names. For demonstration purposes, we’ll define a simple python function that computes a summation of exponential function and returns the results as an array:

def dbexpl(p):
    y = (p['par1']*exp(-p['par2']*t) + p['par3']*exp(-p['par4']*t))
    return y

Of course the python function can be much more complicated, including advanced scipy ( functions or calls to external programs (e.g. External Simulator (FEHM Groundwater Flow Simulator)).

To test that the function does what you expect it to do, you can create a parameter dictionary and pass it to the function:

pars = {'par1':0.5,'par2':0.1,'par3':0.5,'par4':0.1}
print dbexpl(pars)
[  1.00000000e+00   1.35335283e-01   1.83156389e-02   2.47875218e-03

This is only to test the function, MATK will be generating the parameter dictionaries during the model analysis.

If you haven’t added observations to your MATK object, the first time the MATK model is called, observations are automatically created and given default names of obs1, obs2, …, obsN, where N is the number of observations. If you have added observations to your MATK object and your model returns an array, the array ordering must match the order in which you added observations. If your model returns a dictionary, the order is irrelevant. However, if your model returns a dictionary and you have defined observations in your MATK object, your model must return a dictionary with keys that match all the defined observations. An example of dbexpl that returns a dictionary is:

def dbexpl(p):
    y = (p['par1']*exp(-p['par2']*t) + p['par3']*exp(-p['par4']*t))
    ydict = dict([('obs'+str(i+1), v)  for i,v in enumerate(y)])
    return ydict
print dbexpl(pars)
{'obs4': 0.0024787521766663585, 'obs5': 0.00033546262790251185, 'obs2': 0.1353352832366127, 'obs3': 0.018315638888734179, 'obs1': 1.0}

Note that the dictionary is out of order. As mentioned above, this is irrelevant since the keys indicate to which observation the values are associated.

To maintain the order of the returned dictionary, you can return an OrderedDict from the collections package ( included in MATK:

from matk.ordereddict import OrderedDict

def dbexpl(p):
    y = (p['par1']*exp(-p['par2']*t) + p['par3']*exp(-p['par4']*t))
    ydict = OrderedDict([('obs'+str(i+1), v)  for i,v in enumerate(y)])
    return ydict
print dbexpl(pars)
OrderedDict([('obs1', 1.0), ('obs2', 0.1353352832366127), ('obs3', 0.018315638888734179), ('obs4', 0.0024787521766663585), ('obs5', 0.00033546262790251185)])

As mentioned, while dictionary ordering may be desirable, it is not required by MATK.

Create MATK Object

Create an instance of the MATK class (matk) specifying the function created above as the model using a keyword argument:

p = matk.matk(model=dbexpl)

Add Parameters

Add parameters to the model analysis matching those in the MATK model using add_par:


Check current parameter values:

print p.parvalues
[0.5, 0.1, 0.5, 0.1]

and parameter names:

print p.parnames
['par1', 'par2', 'par3', 'par4']

and other useful information:

print p.parmins
[0, 0, 0, 0]
print p.parmaxs
[1, 0.2, 1, 0.2]

You can also access parameters using the MATK pars dictionary:

OrderedDict([('par1', <Parameter 'par1', 0.5, bounds=[0:1]>), ('par2', <Parameter 'par2', 0.1, bounds=[0:0.2]>), ('par3', <Parameter 'par3', 0.5, bounds=[0:1]>), ('par4', <Parameter 'par4', 0.1, bounds=[0:0.2]>)])

Individual parameters can be accessed using the pars dictionary as:

<Parameter 'par1', 0.5, bounds=[0:1]>

Add Observations

Observations are values that you want to compare model results to. These may be measurements that have been collected from the system you are modeling. Let’s assume we have the following measurements for our system:

observations = [ 1., 0.14, 0.021, 2.4e-3, 3.4e-4]

We’ll add these to the model analysis with generic names using add_obs:

for i,o in enumerate(observations): p.add_obs( 'obs'+str(i+1), value=o)

In cases where there are no observations (measurements) for comparison, the value keyword argument can be omitted. Check observation values and names:

print p.obsvalues
[1.0, 0.14, 0.021, 0.0024, 0.00034]
print p.obsnames
['obs1', 'obs2', 'obs3', 'obs4', 'obs5']

Similar to parameters, observations can be accessed using the obs dictionary:

print p.obs
OrderedDict([('obs1', <Observation 'obs1', observed=1.0, weight=1.0>), ('obs2', <Observation 'obs2', observed=0.14, weight=1.0>), ('obs3', <Observation 'obs3', observed=0.021, weight=1.0>), ('obs4', <Observation 'obs4', observed=0.0024, weight=1.0>), ('obs5', <Observation 'obs5', observed=0.00034, weight=1.0>)])
print p.obs['obs1']
<Observation 'obs1', observed=1.0, weight=1.0>
print p.obs['obs1'].value
print p.obs['obs1'].weight

Run Forward Model

A single forward run of the model using the current parameter values can be performed with the forward method as:

sims = p.forward()
print sims
OrderedDict([('obs1', 1.0), ('obs2', 0.1353352832366127), ('obs3', 0.018315638888734179), ('obs4', 0.0024787521766663585), ('obs5', 0.00033546262790251185)])

Now if we look at the obs dictionary, we see that it includes simulated values:

print p.obs
OrderedDict([('obs1', <Observation 'obs1', observed=1.0, simulated=1.0, weight=1.0>), ('obs2', <Observation 'obs2', observed=0.14, simulated=0.1353352832366127, weight=1.0>), ('obs3', <Observation 'obs3', observed=0.021, simulated=0.018315638888734179, weight=1.0>), ('obs4', <Observation 'obs4', observed=0.0024, simulated=0.0024787521766663585, weight=1.0>), ('obs5', <Observation 'obs5', observed=0.00034, simulated=0.00033546262790251185, weight=1.0>)])

The simulated values can be accessed directly also:

print p.simvalues
[1.0, 0.1353352832366127, 0.018315638888734179, 0.0024787521766663585, 0.00033546262790251185]

The sum-of-squares can be calculated using the ssr method:

print p.ssr

You have now completed the most basic model analysis using MATK, the forward model run. The next step is to take a look at the Examples section for details on more useful model analyses involving many forward model runs.