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Diffstat (limited to 'pyspike/PieceWiseLinFunc.py')
| -rw-r--r-- | pyspike/PieceWiseLinFunc.py | 270 |
1 files changed, 270 insertions, 0 deletions
diff --git a/pyspike/PieceWiseLinFunc.py b/pyspike/PieceWiseLinFunc.py new file mode 100644 index 0000000..8faaec4 --- /dev/null +++ b/pyspike/PieceWiseLinFunc.py @@ -0,0 +1,270 @@ +# Class representing piece-wise linear functions. +# Copyright 2014-2015, Mario Mulansky <mario.mulansky@gmx.net> +# Distributed under the BSD License + +from __future__ import absolute_import, print_function + +import numpy as np +import collections +import pyspike + + +############################################################## +# PieceWiseLinFunc +############################################################## +class PieceWiseLinFunc: + """ A class representing a piece-wise linear function. """ + + def __init__(self, x, y1, y2): + """ Constructs the piece-wise linear function. + + :param x: array of length N+1 defining the edges of the intervals of + the pwc function. + :param y1: array of length N defining the function values at the left + of the intervals. + :param y2: array of length N defining the function values at the right + of the intervals. + """ + # convert to array, which also ensures copying + self.x = np.array(x) + self.y1 = np.array(y1) + self.y2 = np.array(y2) + + def __call__(self, t): + """ Returns the function value for the given time t. If t is a list of + times, the corresponding list of values is returned. + + :param: time t, or list of times + :returns: function value(s) at that time(s). + """ + def intermediate_value(x0, x1, y0, y1, x): + """ computes the intermediate value of a linear function """ + return y0 + (y1-y0)*(x-x0)/(x1-x0) + + assert np.all(t >= self.x[0]) and np.all(t <= self.x[-1]), \ + "Invalid time: " + str(t) + + ind = np.searchsorted(self.x, t, side='right') + + if isinstance(t, collections.Sequence): + # t is a sequence of values + # correct the cases t == x[0], t == x[-1] + ind[ind == 0] = 1 + ind[ind == len(self.x)] = len(self.x)-1 + value = intermediate_value(self.x[ind-1], + self.x[ind], + self.y1[ind-1], + self.y2[ind-1], + t) + # correct the values at exact spike times: there the value should + # be the at half of the step + # obtain the 'left' side indices for t + ind_l = np.searchsorted(self.x, t, side='left') + # if left and right side indices differ, the time t has to appear + # in self.x + ind_at_spike = np.logical_and(np.logical_and(ind != ind_l, + ind > 1), + ind < len(self.x)) + # get the corresponding indices for the resulting value array + val_ind = np.arange(len(ind))[ind_at_spike] + # and for the values in self.x, y1, y2 + xy_ind = ind[ind_at_spike] + # the values are defined as the average of the left and right limit + value[val_ind] = 0.5 * (self.y1[xy_ind-1] + self.y2[xy_ind-2]) + return value + else: # t is a single value + # specific check for interval edges + if t == self.x[0]: + return self.y1[0] + if t == self.x[-1]: + return self.y2[-1] + # check if we are on any other exact spike time + if sum(self.x == t) > 0: + # use the middle of the left and right Spike value + return 0.5 * (self.y1[ind-1] + self.y2[ind-2]) + return intermediate_value(self.x[ind-1], + self.x[ind], + self.y1[ind-1], + self.y2[ind-1], + t) + + def copy(self): + """ Returns a copy of itself + + :rtype: :class:`PieceWiseLinFunc` + """ + return PieceWiseLinFunc(self.x, self.y1, self.y2) + + def almost_equal(self, other, decimal=14): + """ Checks if the function is equal to another function up to `decimal` + precision. + + :param other: another :class:`PieceWiseLinFunc` + :returns: True if the two functions are equal up to `decimal` decimals, + False otherwise + :rtype: bool + """ + eps = 10.0**(-decimal) + return np.allclose(self.x, other.x, atol=eps, rtol=0.0) and \ + np.allclose(self.y1, other.y1, atol=eps, rtol=0.0) and \ + np.allclose(self.y2, other.y2, atol=eps, rtol=0.0) + + def get_plottable_data(self): + """ Returns two arrays containing x- and y-coordinates for immeditate + plotting of the piece-wise function. + + :returns: (x_plot, y_plot) containing plottable data + :rtype: pair of np.array + + Example:: + + x, y = f.get_plottable_data() + plt.plot(x, y, '-o', label="Piece-wise const function") + """ + x_plot = np.empty(2*len(self.x)-2) + x_plot[0] = self.x[0] + x_plot[1::2] = self.x[1:] + x_plot[2::2] = self.x[1:-1] + y_plot = np.empty_like(x_plot) + y_plot[0::2] = self.y1 + y_plot[1::2] = self.y2 + return x_plot, y_plot + + def integral(self, interval=None): + """ Returns the integral over the given interval. + + :param interval: integration interval given as a pair of floats, if + None the integral over the whole function is computed. + :type interval: Pair of floats or None. + :returns: the integral + :rtype: float + """ + + def intermediate_value(x0, x1, y0, y1, x): + """ computes the intermediate value of a linear function """ + return y0 + (y1-y0)*(x-x0)/(x1-x0) + + if interval is None: + # no interval given, integrate over the whole spike train + return np.sum((self.x[1:]-self.x[:-1]) * 0.5*(self.y1+self.y2)) + + # find the indices corresponding to the interval + start_ind = np.searchsorted(self.x, interval[0], side='right') + end_ind = np.searchsorted(self.x, interval[1], side='left')-1 + assert start_ind > 0 and end_ind < len(self.x), \ + "Invalid averaging interval" + if start_ind > end_ind: + print(start_ind, end_ind, self.x[start_ind]) + # contribution from between two closest edges + y_x0 = intermediate_value(self.x[start_ind-1], + self.x[start_ind], + self.y1[start_ind-1], + self.y2[start_ind-1], + interval[0]) + y_x1 = intermediate_value(self.x[start_ind-1], + self.x[start_ind], + self.y1[start_ind-1], + self.y2[start_ind-1], + interval[1]) + print(y_x0, y_x1, interval[1] - interval[0]) + integral = (y_x0 + y_x1) * 0.5 * (interval[1] - interval[0]) + print(integral) + else: + # first the contribution from between the indices + integral = np.sum((self.x[start_ind+1:end_ind+1] - + self.x[start_ind:end_ind]) * + 0.5*(self.y1[start_ind:end_ind] + + self.y2[start_ind:end_ind])) + # correction from start to first index + integral += (self.x[start_ind]-interval[0]) * 0.5 * \ + (self.y2[start_ind-1] + + intermediate_value(self.x[start_ind-1], + self.x[start_ind], + self.y1[start_ind-1], + self.y2[start_ind-1], + interval[0])) + # correction from last index to end + integral += (interval[1]-self.x[end_ind]) * 0.5 * \ + (self.y1[end_ind] + + intermediate_value(self.x[end_ind], self.x[end_ind+1], + self.y1[end_ind], self.y2[end_ind], + interval[1] + )) + return integral + + def avrg(self, interval=None): + """ Computes the average of the piece-wise linear function: + :math:`a = 1/T \int_0^T f(x) dx` where T is the interval length. + + :param interval: averaging interval given as a pair of floats, a + sequence of pairs for averaging multiple intervals, or + None, if None the average over the whole function is + computed. + :type interval: Pair, sequence of pairs, or None. + :returns: the average a. + :rtype: float + + """ + + if interval is None: + # no interval given, average over the whole spike train + return self.integral() / (self.x[-1]-self.x[0]) + + # check if interval is as sequence + assert isinstance(interval, collections.Sequence), \ + "Invalid value for `interval`. None, Sequence or Tuple expected." + # check if interval is a sequence of intervals + if not isinstance(interval[0], collections.Sequence): + # just one interval + a = self.integral(interval) / (interval[1]-interval[0]) + else: + # several intervals + a = 0.0 + int_length = 0.0 + for ival in interval: + a += self.integral(ival) + int_length += ival[1] - ival[0] + a /= int_length + return a + + def add(self, f): + """ Adds another PieceWiseLin function to this function. + Note: only functions defined on the same interval can be summed. + + :param f: :class:`PieceWiseLinFunc` function to be added. + :rtype: None + """ + assert self.x[0] == f.x[0], "The functions have different intervals" + assert self.x[-1] == f.x[-1], "The functions have different intervals" + + # python implementation + # from .python_backend import add_piece_wise_lin_python + # self.x, self.y1, self.y2 = add_piece_wise_lin_python( + # self.x, self.y1, self.y2, f.x, f.y1, f.y2) + + # cython version + try: + from .cython.cython_add import add_piece_wise_lin_cython as \ + add_piece_wise_lin_impl + except ImportError: + if not(pyspike.disable_backend_warning): + print("Warning: add_piece_wise_lin_cython not found. Make \ +sure that PySpike is installed by running\n \ +'python setup.py build_ext --inplace'! \n \ +Falling back to slow python backend.") + # use python backend + from .cython.python_backend import add_piece_wise_lin_python as \ + add_piece_wise_lin_impl + + self.x, self.y1, self.y2 = add_piece_wise_lin_impl( + self.x, self.y1, self.y2, f.x, f.y1, f.y2) + + def mul_scalar(self, fac): + """ Multiplies the function with a scalar value + + :param fac: Value to multiply + :type fac: double + :rtype: None + """ + self.y1 *= fac + self.y2 *= fac |