Source code for numa.RootFinder._preAnalysis

import numpy as np
from numa import utils


def preAnalysis1D(function, interval_start, interval_end):
    """Approximate possible roots of a given one-parameter function and the given domain.
This function creates a numpy.linspace and calculates all possible values on that domain. The function is assumed
to be continuous and not positive definit axial symmetric with respect to the y axis in that case. Positions where the sign of the function value changes will be marked as a possible
root area and returned. This method should not be used to approximate roots. It should rather be a tool to further
define the domain space for methods like numa.RootFinder.bisection.


Parameters
----------
function: callable, (e.g f = lambda x: x**2)
    Function to analyze.
interval_start: int
    lower limit of the domain
interval_end: int
    upper limit of the domain

Returns
-------
list
    A list of all x values that are in the near area of a root.

"""
    domain = np.linspace(interval_start, interval_end, 100000)
    f_vals = function(domain)
    sign_switches = list()
    for index in range(1, len(f_vals)):
        if f_vals[index] * f_vals[index-1] < 0:
            sign_switches.append(domain[index])
    if len(sign_switches) == 0:
        return None
    return sign_switches