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381 lines
12 KiB
381 lines
12 KiB
# $Id: fitting.py,v 1.4 2011-04-05 19:20:01 wirawan Exp $
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#
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# wpylib.math.fitting module
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# Created: 20100120
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# Wirawan Purwanto
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#
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# Imported 20100120 from $PWQMC77/expt/Hybrid-proj/analyze-Eh.py
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# (dated 20090323).
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#
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# Some references on fitting:
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# * http://stackoverflow.com/questions/529184/simple-multidimensional-curve-fitting
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# * http://www.scipy.org/Cookbook/OptimizationDemo1 (not as thorough, but maybe useful)
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import numpy
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import scipy.optimize
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from wpylib.db.result_base import result_base
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try:
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import lmfit
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HAS_LMFIT = True
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except ImportError:
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HAS_LMFIT = False
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last_fit_rslt = None
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last_chi_sqr = None
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class fit_result(result_base):
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"""The basic values expected in fit_result are:
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- xopt
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- chi_square
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Optional values:
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- funcalls
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- xerr
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"""
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pass
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def fit_func(Funct, Data=None, Guess=None, Params=None,
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x=None, y=None,
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w=None, dy=None,
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debug=0,
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outfmt=1,
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Funct_hook=None,
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method='leastsq', opts={}):
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"""
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Performs a function fitting.
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The domain of the function is a D-dimensional vector, and the function
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yields a scalar.
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Funct is a python function (or any callable object) with argument list of
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(C, x), where:
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* C is the cofficients (parameters) being adjusted by the fitting process
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(it is a sequence or a 1-D array)
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* x is a 2-D array (or sequence of like nature), say,
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of size "N rows times M columns".
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N is the dimensionality of the domain, while
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M is the number of data points, whose count must be equal to the
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size of y data below.
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For a 2-D fitting, for example, x should be a column array.
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An input guess for the parameters can be specified via Guess argument.
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It is an ordered list of scalar values for these parameters.
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The Params argument is reserved for lmfit-style fitting.
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It is ignored in other cases.
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The "y" array is a 1-D array of length M, which contain the "measured"
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value of the function at every domain point given in "x".
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The "w" or "dy" array (only one of them can be specified in a call),
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if given, specifies either the weight or standard error of the y data.
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If "dy" is specified, then "w" is defined to be (1.0 / dy**2), per usual
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convention.
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Inspect Poly_base, Poly_order2, and other similar function classes in this
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module to see the example of the Funct function.
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The measurement (input) datasets, against which the function is to be fitted,
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can be specified in one of two ways:
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* via x and y arguments. x is a multi-column dataset, where each row is the
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(multidimensional) coordinate of the Funct's domain.
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y is a one-dimensional dataset.
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Or,
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* via Data argument (which is a multi-column dataset, where the first row
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is the "y" argument).
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OUTPUT
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By default, only the fitted parameters are returned.
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To return as complete information as possible, use outfmt=0.
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The return value will be a struct-like object (class: fit_result).
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DEBUGGING
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Debugging and other investigations can be done with "Funct_hook", which,
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if defined, will be called every time right after "Funct" is called.
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It is called with the following signature:
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Funct_hook(C, x, y, f, r)
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where
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f := f(C,x)
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r := f(C,x) - y
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Note that the reference to the hook object is passed as the first argument
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to facilitate object oriented programming.
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SUPPORT FOR LMFIT MODULE
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This routine also supports the lmfit module.
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In this case, the Funct object must supply additional attributes:
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* param_names: an ordered list of parameter names.
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This is used in the case that Params argument is not defined.
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Input parameters can be specified ahead of time in the following ways:
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* If Params is None (default), then unconstrained minimization is done
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and the necessary Parameter objects are created on-the fly.
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* If Params is a Parameters object, then they are used.
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Note that these parameters *will* be clobbered!
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The input Guess parameter can be set to False, in which case Params *must*
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be defined and the initial values will be used as Guess.
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"""
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global last_fit_rslt, last_chi_sqr
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from scipy.optimize import fmin, fmin_bfgs, leastsq, anneal
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# We want to minimize this error:
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if Data != None:
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# an alternative way to specifying x and y
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Data = numpy.asarray(Data)
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y = Data[0]
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x = Data[1:] # possibly multidimensional!
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else:
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x = numpy.asarray(x)
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y = numpy.asarray(y)
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if debug >= 1:
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print "fit_func: using function=%s, minimizer=%s" \
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% (repr(Funct), method)
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if debug >= 10:
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print "fit routine opts = ", opts
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print "Dimensionality of the domain is: ", len(x)
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if method.startswith("lmfit:"):
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if not HAS_LMFIT:
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raise ValueError, \
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"Module lmfit is not found, cannot use `%s' minimization method." \
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% (method,)
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use_lmfit = True
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from lmfit import minimize, Parameters, Parameter
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param_names = Funct.param_names
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if debug >= 10:
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print "param names: ", param_names
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else:
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use_lmfit = False
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if Guess != None:
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pass
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elif hasattr(Funct, "Guess_xy"):
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# Try to provide an initial guess
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Guess = Funct.Guess_xy(x, y)
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elif hasattr(Funct, "Guess"):
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# Try to provide an initial guess
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# This is an older version with y-only argument
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Guess = Funct.Guess(y)
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elif Guess == None: # VERY OLD, DO NOT USE ANYMORE!
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Guess = [ y.mean() ] + [0.0, 0.0] * len(x)
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if use_lmfit:
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if Params == None:
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if debug >= 10:
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print "No input Params given; creating unconstrained params"
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# Creates a default list of Parameters for use later
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assert Guess != False
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Params = Parameters()
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for (g,pn) in zip(Guess, param_names):
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Params.add(pn, value=g)
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else:
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if debug >= 10:
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print "Input Params specified; use them"
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if Guess == None or Guess == False:
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# copy the Params' values to Guess
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Guess = [ Params[pn].value for pn in param_names ]
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else:
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# copy the Guess values onto the Params' values
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for (g,pn) in zip(Guess, param_names):
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Params[pn].value = g
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if debug >= 10:
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print "lmfit guess parameters:"
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for k1 in Params:
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print " - ", Params[k1]
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if debug >= 5:
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print "Guess params:"
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print " ", Guess
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if Funct_hook != None:
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if not hasattr(Funct_hook, "__call__"):
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raise TypeError, "Funct_hook argument must be a callable function."
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def fun_err(CC, xx, yy, ww):
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"""Computes the error of the fitted functional against the
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reference data points:
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* CC = current function parameters
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* xx = domain points of the ("measured") data
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* yy = target points of the ("measured") data
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* ww = weights of the ("measured") data (usually, 1/error**2 of the data)
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"""
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ff = Funct(CC,xx)
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r = (ff - yy) * ww
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Funct_hook(CC, xx, yy, ff, r)
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return r
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elif debug < 20:
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def fun_err(CC, xx, yy, ww):
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ff = Funct(CC,xx)
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r = (ff - yy) * ww
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return r
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else:
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def fun_err(CC, xx, yy, ww):
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ff = Funct(CC,xx)
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r = (ff - yy) * ww
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print " err: %s << %s << %s, %s, %s" % (r, ff, CC, xx, ww)
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return r
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fun_err2 = lambda CC, xx, yy, ww: numpy.sum(abs(fun_err(CC, xx, yy, ww))**2)
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if w != None and dy != None:
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raise TypeError, "Only one of w or dy can be specified."
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if dy != None:
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sqrtw = 1.0 / numpy.asarray(dy)
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elif w != None:
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sqrtw = numpy.sqrt(w)
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else:
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sqrtw = 1.0
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# Full result is stored in rec
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rec = fit_result()
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extra_keys = {}
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chi_sqr = None
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if method == 'leastsq':
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# modified Levenberg-Marquardt algorithm
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rslt = leastsq(fun_err,
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x0=Guess, # initial coefficient guess
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args=(x,y,sqrtw), # data onto which the function is fitted
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full_output=1,
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**opts
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)
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keys = ('xopt', 'cov_x', 'infodict', 'mesg', 'ier') # ier = error message code from MINPACK
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extra_keys = {
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# map the output values to the same keyword as other methods below:
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'funcalls': (lambda : rslt[2]['nfev']),
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}
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# Added estimate of fit parameter uncertainty (matching GNUPLOT parameter
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# uncertainty.
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# The error is estimated to be the diagonal of cov_x, multiplied by the WSSR
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# (chi_square below) and divided by the number of fit degrees of freedom.
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# I used newer scipy.optimize.curve_fit() routine as my cheat sheet here.
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if outfmt == 0:
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if rslt[1] != None and len(y) > len(rslt[0]):
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NDF = len(y) - len(rslt[0])
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extra_keys['xerr'] = (lambda:
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numpy.sqrt(numpy.diagonal(rslt[1]) * rec['chi_square'] / NDF)
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)
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elif method == 'fmin':
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# Nelder-Mead Simplex algorithm
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rslt = fmin(fun_err2,
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x0=Guess, # initial coefficient guess
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args=(x,y,sqrtw), # data onto which the function is fitted
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full_output=1,
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**opts
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)
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keys = ('xopt', 'fopt', 'iter', 'funcalls', 'warnflag', 'allvecs')
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elif method == 'fmin_bfgs' or method == 'bfgs':
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# Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm
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rslt = fmin_bfgs(fun_err2,
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x0=Guess, # initial coefficient guess
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args=(x,y,sqrtw), # data onto which the function is fitted
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full_output=1,
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**opts
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)
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keys = ('xopt', 'fopt', 'funcalls', 'gradcalls', 'warnflag', 'allvecs')
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elif method == 'anneal':
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rslt = anneal(fun_err2,
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x0=Guess, # initial coefficient guess
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args=(x,y,sqrtw), # data onto which the function is fitted
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full_output=1,
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**opts
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)
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keys = ('xopt', 'fopt', 'T', 'funcalls', 'iter', 'accept', 'retval')
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elif use_lmfit:
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submethod = method.split(":",1)[1]
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minrec = minimize(fun_err, Params,
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args=(x,y,sqrtw),
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method=submethod,
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# backend ("real" minimizer) options:
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full_output=1,
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**opts
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)
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xopt = [ Params[k1].value for k1 in param_names ]
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keys = ('xopt', 'minobj', 'params')
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rslt = [ xopt, minrec, Params ]
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# map the output values (in the Minimizer instance, minrec), to
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# the same keyword as other methods for backward compatiblity.
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rec['funcalls'] = minrec.nfev
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try:
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chi_sqr = minrec.chi_sqr
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except:
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pass
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# These seem to be particular to leastsq:
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try:
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rec['ier'] = minrec.ier
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except:
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pass
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try:
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rec['mesg'] = minrec.lmdif_message
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except:
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pass
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try:
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rec['message'] = minrec.message
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except:
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pass
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# Added estimate of fit parameter uncertainty (matching GNUPLOT parameter
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# uncertainty.
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# The error is estimated to be the diagonal of cov_x, multiplied by the WSSR
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# (chi_square below) and divided by the number of fit degrees of freedom.
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# I used newer scipy.optimize.curve_fit() routine as my cheat sheet here.
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if outfmt == 0:
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try:
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has_errorbars = minrec.errorbars
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except:
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has_errorbars = False
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if has_errorbars:
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try:
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rec['xerr'] = [ Params[k1].stderr for k1 in param_names ]
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except:
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# it shouldn't fail like this!
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import warnings
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warnings.warn("wpylib.math.fitting.fit_func: Fail to get standard error of the fit parameters")
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if debug >= 10:
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if 'xerr' in rec:
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print "param errorbars are found:"
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print " ", tuple(rec['xerr'])
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else:
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print "param errorbars are NOT found!"
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else:
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raise ValueError, "Unsupported minimization method: %s" % method
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# Final common post-processing:
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if chi_sqr == None:
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chi_sqr = fun_err2(rslt[0], x, y, sqrtw)
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last_chi_sqr = chi_sqr
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last_fit_rslt = rslt
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if (debug >= 10):
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#print "Fit-message: ", rslt[]
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print "Fit-result:"
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print "\n".join([ "%2d %s" % (ii, rslt[ii]) for ii in xrange(len(rslt)) ])
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if debug >= 1:
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print "params = ", rslt[0]
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print "chi square = ", last_chi_sqr / len(y)
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if outfmt == 0: # outfmt == 0 -- full result.
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rec.update(dict(zip(keys, rslt)))
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rec['chi_square'] = chi_sqr
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rec['fit_method'] = method
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# If there are extra keys, record them here:
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for (k,v) in extra_keys.iteritems():
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rec[k] = v()
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return rec
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elif outfmt == 1:
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return rslt[0]
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else:
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try:
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x = str(outfmt)
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except:
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x = "(?)"
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raise ValueError, "Invalid `outfmt' argument = " + x
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