Source code for Stoner.Util

# -*- coding: utf-8 -*-
"""Stoner.Utils - a module of some slightly experimental routines that use the Stoner classes."""
__all__ = ["split_up_down", "ordinal", "hysteresis_correct"]
import numpy as np
from numpy import max, argmax, mean  # pylint: disable=redefined-builtin
from scipy.stats import sem
from scipy.optimize import fsolve

from .Core import DataFile

from .tools import format_error, make_Data, ordinal
from . import DataFolder
from .analysis.fitting.models.generic import linear

def _step(x, m, c, h):
    """Provide a sloping step function for fitting to the extrema of a hysteresis loop.

        x (array-like):
            Field (x) data of loop.
        m (float):
            susceptibility(slopee) of loop.
        c (float):
            vertical offset of loop.
        h (float):
            Saturatted moement (height) of loop.

        y (Tarray-like):
            Calculated moment of loop.
    mid = (x.max() + x.min()) / 2.0

    X = x - mid
    y = m * x + c + np.sign(X) * h
    return y

def _h_sat_linear(d, i, Ms_vals, Hsat_vals, h_sat_fraction):
    """Determine the saturation field from linear fits to the hysteresis loop.

    This method uses the intercept of the saturated state with zero field portions of the loop.
    from Stoner.analysis.fitting.models.generic import Linear

    Ms, Ms_err, _ = Ms_vals
    Hsat, Hsat_err = Hsat_vals

    # Fit a striaght line to the central fraction of the data
    if i == 1:
        bounds = lambda x, r: np.abs(r.y) < np.abs(Ms) * h_sat_fraction
        bounds = lambda x, r: np.abs(r.y) < np.abs(Ms) * h_sat_fraction
    popt, pcov = d.lmfit(Linear, bounds=bounds)
    perr = np.sqrt(np.diag(pcov))
    popt = popt[:2]
    pferr = perr / popt
    # Pick the positive or negative Ms depending on the up or down loop
    Ms_i = Ms if i == 0 else -Ms
    # Find the intercept
    Hsat[1 - i] = fsolve(lambda x: Linear().func(x, *popt) - Ms_i, 0)[0]
    # Uncertainity is the sum of error in slope * found intercept and error in Ms times slope
    Hsat_err[1 - i] = np.sqrt((Hsat[1 - i] * pferr[1]) ** 2 + (popt[1] * Ms_err) ** 2)

    return (Hsat, Hsat_err)

def _h_sat_susceptibility(d, i, Ms_vals, Hsat_vals, h_sat_fraction):  # pylint: disable=unused-argument
    """Determine the saturation field from the change in local sysceptibility in the looop."""
    Hsat, Hsat_err = Hsat_vals
    xi = d.SG_Filter(order=1)[0, :]
    m, h = d.SG_Filter()
    tmp = np.column_stack((h, m, xi))[4:-4]
    tmp = make_Data(tmp, setas="x.y")
    threshold = tmp.mean(bounds=lambda r: not 7 < r.i < len(tmp) - 7) * h_sat_fraction
    hs = tmp.threshold(threshold, all_vals=True, rising=i != 0, falling=i == 0)  # Get the H_sat value
    Hsat[1 - i] = mean(hs)  # Get the H_sat value
    if hs.size > 1:
        Hsat_err[1 - i] = sem(hs)
        Hsat_err[1 - i] = np.NaN
    return (Hsat, Hsat_err)

def _h_sat_delta_M(d, i, Ms_vals, Hsat_vals, h_sat_fraction):  # pylint: disable=unused-argument
    """Determine the saturation field from the change in magnetisation from Ms."""
    m_sat = Ms_vals[2]
    Hsat, Hsat_err = Hsat_vals
    m, h = d.SG_Filter()
    tmp = np.column_stack((h, m))[4:-4]
    tmp = make_Data(tmp, setas="xy")
    threshold = m_sat[i]
    hs = tmp.threshold(threshold, all_vals=True, rising=True, falling=True).view(np.ndarray)  # Get the H_sat value
    if hs.size > 1:
        hs = hs[np.argmin(np.abs(hs))]
    Hsat[1 - i] = hs  # Get the H_sat value
    Hsat_err[1 - i] = np.NaN
    return (Hsat, Hsat_err)

def _up_down(data):
    """Split data d into rising and falling sections and then add and sort the two sets.

    This routine searches for the local maxima and minima in the x-axis data by identifying points
    where the x-data is more than 95% of the total span from the mid-point. It thenuses this to identify
    ranges of rows where the x value passes from one extreme to the other and splits the data file up on
    that basis. This assumes that the x-data is reasonably well behaved in the the increments between
    successive x-values are larger than the noise in x. This will work best if the x value is derived from a set value
    rather than the read-back value.

        data (Data):
            DataFile like object with x and y columns set

        (Data, Data):
            Tuple of two DataFile like instances for the rising and falling data.
    # Calculate x span and mid-point for working out limits to search for maxima.
    lx, hx = data.span(data.setas.xcol)
    mid = (lx + hx) / 2.0
    span = hx - lx
    high = data.x > mid + 0.45 * span
    low = data.x < mid - 0.45 * span

    # Locate points where we cross a threhold
    t = np.zeros((2, len(data) + 2), dtype=bool)
    t[0, 1:-1] = high
    t[1, 1:-1] = low
    t = np.diff(t)

    # Find  the indiices of the highest and lowest extrema
    high_i = np.arange(len(data) + 1, dtype=int)[t[0, :]]
    low_i = np.arange(len(data) + 1, dtype=int)[t[1, :]]
    if low_i.size > 2:
        low_i = np.reshape(low_i, (2, -1)).mean(axis=1)
        low_i = np.array(low_i.mean())
    if high_i.size > 2:
        high_i = np.reshape(high_i, (2, -1)).mean(axis=1)
        high_i = np.array(high_i.mean())
    # Build a sorted list of extrema positions + the start and end of the data
    indices = np.unique(np.append(low_i, np.append(high_i, np.array([0, len(data) - 1]))))
    indices = np.ceil(indices).astype(int)
    if indices[-1] >= len(data):  # Remove possible over-range element
        indices = indices[0:-1]

    # Build a boolean array to index the data for rows that where x is increasing
    rising = np.zeros(len(data), dtype=bool)
    for ix, iy in zip(indices[:-1], indices[1:]):
        if data.x[iy] > data.x[ix]:
            rising[ix:iy] = True

    # Clone the data and select rows that are either rising or falling in the two clones.
    up = data.clone =[rising]
    down = data.clone =[~rising]
    # Done.
    return up, down

[docs]def split_up_down(data, col=None, folder=None): """Split the DataFile data into several files where the column *col* is either rising or falling. Args: data (:py:class:`Stoner.Core.DataFile`): object containign the data to be sorted col (index): is something that :py:meth:`Stoner.Core.DataFile.find_col` can use folder (:py:class:`Stoner.folders.DataFolder` or None): if this is an instance of :py:class:`Stoner.folders.DataFolder` then add rising and falling files to groups of this DataFolder, otherwise create a new one Returns: (:py:class:`Sonter.Folder.DataFolder`): with two groups, rising and falling """ a = make_Data(data) if col is None: _ = a._col_args() col = _.xcol width = int(len(a) / 10) if width % 2 == 0: # Ensure the window for Satvisky Golay filter is odd width += 1 setas = a.setas.clone a.setas = "" peaks = list(a.peaks(ycol=col, width=width, full_data=False)) troughs = list(a.peaks(ycol=col, width=width, peaks=False, troughs=True, full_data=False)) a.setas = setas if peaks and troughs: # Ok more than up down here order = peaks[0] < troughs[0] elif peaks: # Rise then fall order = True elif troughs: # Fall then rise order = False else: # No peaks or troughs so just return a single rising ret = DataFolder(readlist=False) ret += data return ret splits = [0, len(a)] splits.extend(peaks) splits.extend(troughs) splits.sort() splits = [int(s) for s in splits] if not isinstance(folder, DataFolder): # Create a new DataFolder object output = DataFolder(readlist=False) else: output = folder output.add_group("rising") output.add_group("falling") if order: risefall = ["rising", "falling"] else: risefall = ["falling", "rising"] for i in range(len(splits) - 1): working = data.clone =[splits[i] : splits[i + 1], :] output.groups[risefall[i % 2]].append(working) return output
Hickeyify = format_error
[docs]def hysteresis_correct(data, **kargs): """Peform corrections to a hysteresis loop. Args: data (Data): The data containing the hysteresis loop. The :py:attr:`DataFile.setas` attribute should be set to give the H and M axes as x and y. Keyword Arguments: correct_background (bool): Correct for a diamagnetic or paramagnetic background to the hystersis loop also recentres the loop about zero moment (default True). correct_H (bool): Finds the co-ercive fields and sets them to be equal and opposite. If the loop is sysmmetric this will remove any offset in filed due to trapped flux (default True) saturated_fraction (float): The fraction of the horizontal (field) range where the moment can be assumed to be fully saturated. If an integer is given it will use that many data points at the end of the loop. h_sat_method (str): The method used to determine thwe saturation field. Options are - - "linear_intercept" (default): Fit a straight line to the central region of each branch of the loop and look at the intercept with the relevant saturation moment. - "delta_M": Look for a field where the moment has changed by *h_sat_fraction* times the error in M_s. - "susceptibility" - Calcualte H_sat from where the susceptibility changes by 1% of the average susceptibility h_sat_fraction (float): The central fraction of the saturation moment that is used for calculating the saturation field. Defaults to 0.5 xcol (column index): Column with the x data in it ycol (column_index): Column with the y data in it setas (string or iterable): Column assignments. Returns: (:py:class:`Stoner.Data`): The original loop with the x and y columns replaced with corrected data and extra metadata added to give the background suceptibility, offset in moment, co-ercive fields and saturation magnetisation. """ if isinstance(data, DataFile): cls = type(data) else: cls = make_Data(None) data = cls(data) # Get other keyword arguments correct_background = kargs.pop("correct_background", True) correct_H = kargs.pop("correct_H", True) saturation_fraction = kargs.pop("saturated_fraction", 0.2) h_sat_method = kargs.pop("h_sat_method", "linear_intercept") h_sat_fraction = kargs.pop("h_sat_fraction", 0.5 if h_sat_method == "linear_intercept" else 2.0) hsat_methods = { "linear_intercept": _h_sat_linear, "susceptibility": _h_sat_susceptibility, "delta_M": _h_sat_delta_M, } if callable(h_sat_method) or h_sat_method in hsat_methods: h_sat_method = hsat_methods.get(h_sat_method, h_sat_method) else: raise ValueError("Saturation field method not recognized!") for k in kargs: try: setattr(data, k, kargs[k]) except AttributeError: if data.debug: print("Error setting attribute from keyword {k}={args[k]}") if "setas" in kargs: # Allow us to override the setas variable data.setas = kargs.pop("setas") xcol = kargs.pop("xcol", data.setas.xcol) ycol = kargs.pop("ycol", data.setas.ycol) # Get xcol and ycols from kargs if specified _ = data._col_args(xcol=xcol, ycol=ycol) data.setas(x=_.xcol, y=_.ycol, reset=False) # Split into two sets of data: up, down = _up_down(data) mid = (data.x.max() + data.x.min()) / 2.0 span = data.x.max() - data.x.min() low = mid - span * (1 - saturation_fraction) / 2 high = mid + span * (1 - saturation_fraction) / 2 popt, pcov = data.curve_fit(_step, bounds=lambda x, r: not low < x < high) perr = np.sqrt(np.diag(pcov)) Ms = popt[2] Ms_err = perr[2] data["Ms"] = Ms # mean(Ms) data["Ms Error"] = Ms_err data["Offset Moment"] = popt[1] data["Offset Moment Error"] = perr[1] data["Background susceptibility"] = popt[0] data["Background Susceptibility Error"] = perr[0] if correct_background: fixes = [data, up, down] else: fixes = [up, down] m = popt[0] c = popt[1] - m * mid for d in fixes: d.y = d.y - linear(d.x, c, m) Hc = [None, None] Hc_err = [None, None] Hsat = [None, None] Hsat_err = [None, None] Mr = [None, None] Mr_err = [None, None] m_sat = [Ms - h_sat_fraction * Ms_err, -Ms + h_sat_fraction * Ms_err] single_side = False for i, d in enumerate([up, down]): if len(d) < 2: single_side = True continue hc = d.threshold(0.0, all_vals=True, rising=i == 0, falling=i != 0) # Get the Hc value Hc[i] = mean(hc) if hc.size > 1: Hc_err[i] = sem(hc) Hsat, Hsat_err = h_sat_method(d, i, (Ms, Ms_err, m_sat), (Hsat, Hsat_err), h_sat_fraction) mr = d.threshold(0.0, col=_.xcol, xcol=_.ycol, all_vals=True, rising=True, falling=True) Mr[i] = mean(mr) if mr.size > 1: Mr_err[i] = sem(mr) if correct_H and not single_side: Hc_mean = mean(Hc) for d in [data, up, down]: d.x = d.x - Hc_mean data["Exchange Bias offset"] = Hc_mean else: Hc_mean = 0.0 if not single_side: data["Hc"] = (Hc[1] - Hc_mean, Hc[0] - Hc_mean) data["Hc_mean"] = np.abs(np.array(Hc)).mean() data["Hsat"] = (Hsat[1] - Hc_mean, Hsat[0] - Hc_mean) data["Hsat Error"] = (Hsat_err[1], Hsat_err[0]) data["Hsat_mean"] = np.abs(np.array(Hsat)).mean() data["Hsat_mean Error"] = np.sqrt(np.array(Hsat_err) ** 2)[0] / 2.0 else: data["Hc"] = [x for x in Hc if x is not None] data["Hc_mean"] = abs(data["Hc"][0]) data["Hsat"] = [x for x in Hsat if x is not None] data["Hsat Error"] = [x for x in Hsat_err if x is not None] data["Hsat_mean"] = abs(data["Hsat"][0]) data["Hsat_mean Error"] = abs(data["Hsat Error"][0]) data["Remenance"] = Mr bh = (-data.x) * data.y i = argmax(bh) data["BH_Max"] = max(bh) data["BH_Max_H"] = data.x[i] data["Area"] = data.integrate(output="result") return cls(data)