find

find(x, y, /, axis=- 1, axis_track=None, track=True, diff=None, which='both', centered=True, **kwargs)[source]

Find the location of zero values or extrema for a given data array.

Parameters

  • x (array-like) – The coordinates.

  • y (array-like) – The data for which we find zeros.

  • axis (int, optional) – Axis along which zeros are found and (optionally) derivatives are taken.

  • axis_track (int, optional) – Axis along which zeros taken along axis are “tracked”. Default is the last position not occupied by axis.

  • track (bool, optional) – Whether to track zeros. If False they are added in the order they appeared.

  • diff (int, optional) – How many times to differentiate along the axis.

  • which ({‘negpos’, ‘posneg’, ‘both’}, optional) – Whether to find values that go from negative to positive, positive to negative, or both.

  • centered (bool, optional) – If False, use half-level differentiation rather than centered differentiation. Gives more accurate locations but less accurate values.

  • **kwargs – Passed to linetrack and used to group the locations into coherent tracks.

Returns

  • x0s (array-like) – The zero locations.

  • y0s (array-like) – The zero values. If diff == 0 these should all be equal to zero up to floating point precision. Otherwise these are the minima and maxima corresponding to the zero derivative locations.

Examples

>>> import numpy as np
>>> import xarray as xr
>>> import climopy as climo
>>> state = np.random.RandomState(51423)
>>> ureg = climo.ureg
>>> x = np.arange(100)
>>> y = np.sort(state.rand(50, 10) - 0.5, axis=0)
>>> y = np.concatenate((y, y[::-1, :]), axis=0)
>>> xarr = xr.DataArray(
...     x * ureg.s,
...     dims=('x',), attrs={'long_name': 'x coordinate'}
... )
>>> yarr = xr.DataArray(
...     y * ureg.m, name='variable',
...     dims=('x', 'y'), coords={'x': xarr.climo.dequantify()}
... )
>>> x0s, y0s = climo.find(xarr, yarr, axis=0, ntrack=2)
>>> x0s
<xarray.DataArray 'x' (track: 2, y: 10)>
<Quantity([[25.56712412 17.1468964  25.94590963 24.43748793 25.96456694 23.50805224
  24.26007638 25.76728476 26.30359681 22.41433647]
 [73.43287588 81.8531036  73.05409037 74.56251207 73.03543306 75.49194776
  74.73992362 73.23271524 72.69640319 76.58566353]], 'second')>
Dimensions without coordinates: track, y
Attributes:
    long_name:  x coordinate