관리-도구

편집 파일: function_base.py

from __future__ import division, absolute_import, print_function import warnings import operator from . import numeric as _nx from .numeric import (result_type, NaN, shares_memory, MAY_SHARE_BOUNDS, TooHardError,asanyarray) __all__ = ['logspace', 'linspace', 'geomspace'] def _index_deprecate(i, stacklevel=2): try: i = operator.index(i) except TypeError: msg = ("object of type {} cannot be safely interpreted as " "an integer.".format(type(i))) i = int(i) stacklevel += 1 warnings.warn(msg, DeprecationWarning, stacklevel=stacklevel) return i def linspace(start, stop, num=50, endpoint=True, retstep=False, dtype=None): """ Return evenly spaced numbers over a specified interval. Returns `num` evenly spaced samples, calculated over the interval [`start`, `stop`]. The endpoint of the interval can optionally be excluded. Parameters ---------- start : scalar The starting value of the sequence. stop : scalar The end value of the sequence, unless `endpoint` is set to False. In that case, the sequence consists of all but the last of ``num + 1`` evenly spaced samples, so that `stop` is excluded. Note that the step size changes when `endpoint` is False. num : int, optional Number of samples to generate. Default is 50. Must be non-negative. endpoint : bool, optional If True, `stop` is the last sample. Otherwise, it is not included. Default is True. retstep : bool, optional If True, return (`samples`, `step`), where `step` is the spacing between samples. dtype : dtype, optional The type of the output array. If `dtype` is not given, infer the data type from the other input arguments. .. versionadded:: 1.9.0 Returns ------- samples : ndarray There are `num` equally spaced samples in the closed interval ``[start, stop]`` or the half-open interval ``[start, stop)`` (depending on whether `endpoint` is True or False). step : float, optional Only returned if `retstep` is True Size of spacing between samples. See Also -------- arange : Similar to `linspace`, but uses a step size (instead of the number of samples). logspace : Samples uniformly distributed in log space. Examples -------- >>> np.linspace(2.0, 3.0, num=5) array([ 2. , 2.25, 2.5 , 2.75, 3. ]) >>> np.linspace(2.0, 3.0, num=5, endpoint=False) array([ 2. , 2.2, 2.4, 2.6, 2.8]) >>> np.linspace(2.0, 3.0, num=5, retstep=True) (array([ 2. , 2.25, 2.5 , 2.75, 3. ]), 0.25) Graphical illustration: >>> import matplotlib.pyplot as plt >>> N = 8 >>> y = np.zeros(N) >>> x1 = np.linspace(0, 10, N, endpoint=True) >>> x2 = np.linspace(0, 10, N, endpoint=False) >>> plt.plot(x1, y, 'o') [<matplotlib.lines.Line2D object at 0x...>] >>> plt.plot(x2, y + 0.5, 'o') [<matplotlib.lines.Line2D object at 0x...>] >>> plt.ylim([-0.5, 1]) (-0.5, 1) >>> plt.show() """ # 2016-02-25, 1.12 num = _index_deprecate(num) if num < 0: raise ValueError("Number of samples, %s, must be non-negative." % num) div = (num - 1) if endpoint else num # Convert float/complex array scalars to float, gh-3504 # and make sure one can use variables that have an __array_interface__, gh-6634 start = asanyarray(start) * 1.0 stop = asanyarray(stop) * 1.0 dt = result_type(start, stop, float(num)) if dtype is None: dtype = dt y = _nx.arange(0, num, dtype=dt) delta = stop - start if num > 1: step = delta / div if step == 0: # Special handling for denormal numbers, gh-5437 y /= div y = y * delta else: # One might be tempted to use faster, in-place multiplication here, # but this prevents step from overriding what class is produced, # and thus prevents, e.g., use of Quantities; see gh-7142. y = y * step else: # 0 and 1 item long sequences have an undefined step step = NaN # Multiply with delta to allow possible override of output class. y = y * delta y += start if endpoint and num > 1: y[-1] = stop if retstep: return y.astype(dtype, copy=False), step else: return y.astype(dtype, copy=False) def logspace(start, stop, num=50, endpoint=True, base=10.0, dtype=None): """ Return numbers spaced evenly on a log scale. In linear space, the sequence starts at ``base ** start`` (`base` to the power of `start`) and ends with ``base ** stop`` (see `endpoint` below). Parameters ---------- start : float ``base ** start`` is the starting value of the sequence. stop : float ``base ** stop`` is the final value of the sequence, unless `endpoint` is False. In that case, ``num + 1`` values are spaced over the interval in log-space, of which all but the last (a sequence of length `num`) are returned. num : integer, optional Number of samples to generate. Default is 50. endpoint : boolean, optional If true, `stop` is the last sample. Otherwise, it is not included. Default is True. base : float, optional The base of the log space. The step size between the elements in ``ln(samples) / ln(base)`` (or ``log_base(samples)``) is uniform. Default is 10.0. dtype : dtype The type of the output array. If `dtype` is not given, infer the data type from the other input arguments. Returns ------- samples : ndarray `num` samples, equally spaced on a log scale. See Also -------- arange : Similar to linspace, with the step size specified instead of the number of samples. Note that, when used with a float endpoint, the endpoint may or may not be included. linspace : Similar to logspace, but with the samples uniformly distributed in linear space, instead of log space. geomspace : Similar to logspace, but with endpoints specified directly. Notes ----- Logspace is equivalent to the code >>> y = np.linspace(start, stop, num=num, endpoint=endpoint) ... # doctest: +SKIP >>> power(base, y).astype(dtype) ... # doctest: +SKIP Examples -------- >>> np.logspace(2.0, 3.0, num=4) array([ 100. , 215.443469 , 464.15888336, 1000. ]) >>> np.logspace(2.0, 3.0, num=4, endpoint=False) array([ 100. , 177.827941 , 316.22776602, 562.34132519]) >>> np.logspace(2.0, 3.0, num=4, base=2.0) array([ 4. , 5.0396842 , 6.34960421, 8. ]) Graphical illustration: >>> import matplotlib.pyplot as plt >>> N = 10 >>> x1 = np.logspace(0.1, 1, N, endpoint=True) >>> x2 = np.logspace(0.1, 1, N, endpoint=False) >>> y = np.zeros(N) >>> plt.plot(x1, y, 'o') [<matplotlib.lines.Line2D object at 0x...>] >>> plt.plot(x2, y + 0.5, 'o') [<matplotlib.lines.Line2D object at 0x...>] >>> plt.ylim([-0.5, 1]) (-0.5, 1) >>> plt.show() """ y = linspace(start, stop, num=num, endpoint=endpoint) if dtype is None: return _nx.power(base, y) return _nx.power(base, y).astype(dtype) def geomspace(start, stop, num=50, endpoint=True, dtype=None): """ Return numbers spaced evenly on a log scale (a geometric progression). This is similar to `logspace`, but with endpoints specified directly. Each output sample is a constant multiple of the previous. Parameters ---------- start : scalar The starting value of the sequence. stop : scalar The final value of the sequence, unless `endpoint` is False. In that case, ``num + 1`` values are spaced over the interval in log-space, of which all but the last (a sequence of length `num`) are returned. num : integer, optional Number of samples to generate. Default is 50. endpoint : boolean, optional If true, `stop` is the last sample. Otherwise, it is not included. Default is True. dtype : dtype The type of the output array. If `dtype` is not given, infer the data type from the other input arguments. Returns ------- samples : ndarray `num` samples, equally spaced on a log scale. See Also -------- logspace : Similar to geomspace, but with endpoints specified using log and base. linspace : Similar to geomspace, but with arithmetic instead of geometric progression. arange : Similar to linspace, with the step size specified instead of the number of samples. Notes ----- If the inputs or dtype are complex, the output will follow a logarithmic spiral in the complex plane. (There are an infinite number of spirals passing through two points; the output will follow the shortest such path.) Examples -------- >>> np.geomspace(1, 1000, num=4) array([ 1., 10., 100., 1000.]) >>> np.geomspace(1, 1000, num=3, endpoint=False) array([ 1., 10., 100.]) >>> np.geomspace(1, 1000, num=4, endpoint=False) array([ 1. , 5.62341325, 31.6227766 , 177.827941 ]) >>> np.geomspace(1, 256, num=9) array([ 1., 2., 4., 8., 16., 32., 64., 128., 256.]) Note that the above may not produce exact integers: >>> np.geomspace(1, 256, num=9, dtype=int) array([ 1, 2, 4, 7, 16, 32, 63, 127, 256]) >>> np.around(np.geomspace(1, 256, num=9)).astype(int) array([ 1, 2, 4, 8, 16, 32, 64, 128, 256]) Negative, decreasing, and complex inputs are allowed: >>> np.geomspace(1000, 1, num=4) array([ 1000., 100., 10., 1.]) >>> np.geomspace(-1000, -1, num=4) array([-1000., -100., -10., -1.]) >>> np.geomspace(1j, 1000j, num=4) # Straight line array([ 0. +1.j, 0. +10.j, 0. +100.j, 0.+1000.j]) >>> np.geomspace(-1+0j, 1+0j, num=5) # Circle array([-1.00000000+0.j , -0.70710678+0.70710678j, 0.00000000+1.j , 0.70710678+0.70710678j, 1.00000000+0.j ]) Graphical illustration of ``endpoint`` parameter: >>> import matplotlib.pyplot as plt >>> N = 10 >>> y = np.zeros(N) >>> plt.semilogx(np.geomspace(1, 1000, N, endpoint=True), y + 1, 'o') >>> plt.semilogx(np.geomspace(1, 1000, N, endpoint=False), y + 2, 'o') >>> plt.axis([0.5, 2000, 0, 3]) >>> plt.grid(True, color='0.7', linestyle='-', which='both', axis='both') >>> plt.show() """ if start == 0 or stop == 0: raise ValueError('Geometric sequence cannot include zero') dt = result_type(start, stop, float(num)) if dtype is None: dtype = dt else: # complex to dtype('complex128'), for instance dtype = _nx.dtype(dtype) # Avoid negligible real or imaginary parts in output by rotating to # positive real, calculating, then undoing rotation out_sign = 1 if start.real == stop.real == 0: start, stop = start.imag, stop.imag out_sign = 1j * out_sign if _nx.sign(start) == _nx.sign(stop) == -1: start, stop = -start, -stop out_sign = -out_sign # Promote both arguments to the same dtype in case, for instance, one is # complex and another is negative and log would produce NaN otherwise start = start + (stop - stop) stop = stop + (start - start) if _nx.issubdtype(dtype, complex): start = start + 0j stop = stop + 0j log_start = _nx.log10(start) log_stop = _nx.log10(stop) result = out_sign * logspace(log_start, log_stop, num=num, endpoint=endpoint, base=10.0, dtype=dtype) return result.astype(dtype)