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diff DEPENDENCIES/mingw32/Python27/Lib/site-packages/numpy/fft/fftpack.py @ 87:2a2c65a20a8b
Add Python libs and headers
| author | Chris Cannam |
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| date | Wed, 25 Feb 2015 14:05:22 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/DEPENDENCIES/mingw32/Python27/Lib/site-packages/numpy/fft/fftpack.py Wed Feb 25 14:05:22 2015 +0000 @@ -0,0 +1,1169 @@ +""" +Discrete Fourier Transforms + +Routines in this module: + +fft(a, n=None, axis=-1) +ifft(a, n=None, axis=-1) +rfft(a, n=None, axis=-1) +irfft(a, n=None, axis=-1) +hfft(a, n=None, axis=-1) +ihfft(a, n=None, axis=-1) +fftn(a, s=None, axes=None) +ifftn(a, s=None, axes=None) +rfftn(a, s=None, axes=None) +irfftn(a, s=None, axes=None) +fft2(a, s=None, axes=(-2,-1)) +ifft2(a, s=None, axes=(-2, -1)) +rfft2(a, s=None, axes=(-2,-1)) +irfft2(a, s=None, axes=(-2, -1)) + +i = inverse transform +r = transform of purely real data +h = Hermite transform +n = n-dimensional transform +2 = 2-dimensional transform +(Note: 2D routines are just nD routines with different default +behavior.) + +The underlying code for these functions is an f2c-translated and modified +version of the FFTPACK routines. + +""" +from __future__ import division, absolute_import, print_function + +__all__ = ['fft', 'ifft', 'rfft', 'irfft', 'hfft', 'ihfft', 'rfftn', + 'irfftn', 'rfft2', 'irfft2', 'fft2', 'ifft2', 'fftn', 'ifftn'] + +from numpy.core import asarray, zeros, swapaxes, shape, conjugate, \ + take +from . import fftpack_lite as fftpack + +_fft_cache = {} +_real_fft_cache = {} + +def _raw_fft(a, n=None, axis=-1, init_function=fftpack.cffti, + work_function=fftpack.cfftf, fft_cache = _fft_cache ): + a = asarray(a) + + if n is None: + n = a.shape[axis] + + if n < 1: + raise ValueError("Invalid number of FFT data points (%d) specified." % n) + + try: + # Thread-safety note: We rely on list.pop() here to atomically + # retrieve-and-remove a wsave from the cache. This ensures that no + # other thread can get the same wsave while we're using it. + wsave = fft_cache.setdefault(n, []).pop() + except (IndexError): + wsave = init_function(n) + + if a.shape[axis] != n: + s = list(a.shape) + if s[axis] > n: + index = [slice(None)]*len(s) + index[axis] = slice(0, n) + a = a[index] + else: + index = [slice(None)]*len(s) + index[axis] = slice(0, s[axis]) + s[axis] = n + z = zeros(s, a.dtype.char) + z[index] = a + a = z + + if axis != -1: + a = swapaxes(a, axis, -1) + r = work_function(a, wsave) + if axis != -1: + r = swapaxes(r, axis, -1) + + # As soon as we put wsave back into the cache, another thread could pick it + # up and start using it, so we must not do this until after we're + # completely done using it ourselves. + fft_cache[n].append(wsave) + + return r + + +def fft(a, n=None, axis=-1): + """ + Compute the one-dimensional discrete Fourier Transform. + + This function computes the one-dimensional *n*-point discrete Fourier + Transform (DFT) with the efficient Fast Fourier Transform (FFT) + algorithm [CT]. + + Parameters + ---------- + a : array_like + Input array, can be complex. + n : int, optional + Length of the transformed axis of the output. + If `n` is smaller than the length of the input, the input is cropped. + If it is larger, the input is padded with zeros. If `n` is not given, + the length of the input along the axis specified by `axis` is used. + axis : int, optional + Axis over which to compute the FFT. If not given, the last axis is + used. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axis + indicated by `axis`, or the last one if `axis` is not specified. + + Raises + ------ + IndexError + if `axes` is larger than the last axis of `a`. + + See Also + -------- + numpy.fft : for definition of the DFT and conventions used. + ifft : The inverse of `fft`. + fft2 : The two-dimensional FFT. + fftn : The *n*-dimensional FFT. + rfftn : The *n*-dimensional FFT of real input. + fftfreq : Frequency bins for given FFT parameters. + + Notes + ----- + FFT (Fast Fourier Transform) refers to a way the discrete Fourier + Transform (DFT) can be calculated efficiently, by using symmetries in the + calculated terms. The symmetry is highest when `n` is a power of 2, and + the transform is therefore most efficient for these sizes. + + The DFT is defined, with the conventions used in this implementation, in + the documentation for the `numpy.fft` module. + + References + ---------- + .. [CT] Cooley, James W., and John W. Tukey, 1965, "An algorithm for the + machine calculation of complex Fourier series," *Math. Comput.* + 19: 297-301. + + Examples + -------- + >>> np.fft.fft(np.exp(2j * np.pi * np.arange(8) / 8)) + array([ -3.44505240e-16 +1.14383329e-17j, + 8.00000000e+00 -5.71092652e-15j, + 2.33482938e-16 +1.22460635e-16j, + 1.64863782e-15 +1.77635684e-15j, + 9.95839695e-17 +2.33482938e-16j, + 0.00000000e+00 +1.66837030e-15j, + 1.14383329e-17 +1.22460635e-16j, + -1.64863782e-15 +1.77635684e-15j]) + + >>> import matplotlib.pyplot as plt + >>> t = np.arange(256) + >>> sp = np.fft.fft(np.sin(t)) + >>> freq = np.fft.fftfreq(t.shape[-1]) + >>> plt.plot(freq, sp.real, freq, sp.imag) + [<matplotlib.lines.Line2D object at 0x...>, <matplotlib.lines.Line2D object at 0x...>] + >>> plt.show() + + In this example, real input has an FFT which is Hermitian, i.e., symmetric + in the real part and anti-symmetric in the imaginary part, as described in + the `numpy.fft` documentation. + + """ + + return _raw_fft(a, n, axis, fftpack.cffti, fftpack.cfftf, _fft_cache) + + +def ifft(a, n=None, axis=-1): + """ + Compute the one-dimensional inverse discrete Fourier Transform. + + This function computes the inverse of the one-dimensional *n*-point + discrete Fourier transform computed by `fft`. In other words, + ``ifft(fft(a)) == a`` to within numerical accuracy. + For a general description of the algorithm and definitions, + see `numpy.fft`. + + The input should be ordered in the same way as is returned by `fft`, + i.e., ``a[0]`` should contain the zero frequency term, + ``a[1:n/2+1]`` should contain the positive-frequency terms, and + ``a[n/2+1:]`` should contain the negative-frequency terms, in order of + decreasingly negative frequency. See `numpy.fft` for details. + + Parameters + ---------- + a : array_like + Input array, can be complex. + n : int, optional + Length of the transformed axis of the output. + If `n` is smaller than the length of the input, the input is cropped. + If it is larger, the input is padded with zeros. If `n` is not given, + the length of the input along the axis specified by `axis` is used. + See notes about padding issues. + axis : int, optional + Axis over which to compute the inverse DFT. If not given, the last + axis is used. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axis + indicated by `axis`, or the last one if `axis` is not specified. + + Raises + ------ + IndexError + If `axes` is larger than the last axis of `a`. + + See Also + -------- + numpy.fft : An introduction, with definitions and general explanations. + fft : The one-dimensional (forward) FFT, of which `ifft` is the inverse + ifft2 : The two-dimensional inverse FFT. + ifftn : The n-dimensional inverse FFT. + + Notes + ----- + If the input parameter `n` is larger than the size of the input, the input + is padded by appending zeros at the end. Even though this is the common + approach, it might lead to surprising results. If a different padding is + desired, it must be performed before calling `ifft`. + + Examples + -------- + >>> np.fft.ifft([0, 4, 0, 0]) + array([ 1.+0.j, 0.+1.j, -1.+0.j, 0.-1.j]) + + Create and plot a band-limited signal with random phases: + + >>> import matplotlib.pyplot as plt + >>> t = np.arange(400) + >>> n = np.zeros((400,), dtype=complex) + >>> n[40:60] = np.exp(1j*np.random.uniform(0, 2*np.pi, (20,))) + >>> s = np.fft.ifft(n) + >>> plt.plot(t, s.real, 'b-', t, s.imag, 'r--') + [<matplotlib.lines.Line2D object at 0x...>, <matplotlib.lines.Line2D object at 0x...>] + >>> plt.legend(('real', 'imaginary')) + <matplotlib.legend.Legend object at 0x...> + >>> plt.show() + + """ + + a = asarray(a).astype(complex) + if n is None: + n = shape(a)[axis] + return _raw_fft(a, n, axis, fftpack.cffti, fftpack.cfftb, _fft_cache) / n + + +def rfft(a, n=None, axis=-1): + """ + Compute the one-dimensional discrete Fourier Transform for real input. + + This function computes the one-dimensional *n*-point discrete Fourier + Transform (DFT) of a real-valued array by means of an efficient algorithm + called the Fast Fourier Transform (FFT). + + Parameters + ---------- + a : array_like + Input array + n : int, optional + Number of points along transformation axis in the input to use. + If `n` is smaller than the length of the input, the input is cropped. + If it is larger, the input is padded with zeros. If `n` is not given, + the length of the input along the axis specified by `axis` is used. + axis : int, optional + Axis over which to compute the FFT. If not given, the last axis is + used. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axis + indicated by `axis`, or the last one if `axis` is not specified. + If `n` is even, the length of the transformed axis is ``(n/2)+1``. + If `n` is odd, the length is ``(n+1)/2``. + + Raises + ------ + IndexError + If `axis` is larger than the last axis of `a`. + + See Also + -------- + numpy.fft : For definition of the DFT and conventions used. + irfft : The inverse of `rfft`. + fft : The one-dimensional FFT of general (complex) input. + fftn : The *n*-dimensional FFT. + rfftn : The *n*-dimensional FFT of real input. + + Notes + ----- + When the DFT is computed for purely real input, the output is + Hermitian-symmetric, i.e. the negative frequency terms are just the complex + conjugates of the corresponding positive-frequency terms, and the + negative-frequency terms are therefore redundant. This function does not + compute the negative frequency terms, and the length of the transformed + axis of the output is therefore ``n//2 + 1``. + + When ``A = rfft(a)`` and fs is the sampling frequency, ``A[0]`` contains + the zero-frequency term 0*fs, which is real due to Hermitian symmetry. + + If `n` is even, ``A[-1]`` contains the term representing both positive + and negative Nyquist frequency (+fs/2 and -fs/2), and must also be purely + real. If `n` is odd, there is no term at fs/2; ``A[-1]`` contains + the largest positive frequency (fs/2*(n-1)/n), and is complex in the + general case. + + If the input `a` contains an imaginary part, it is silently discarded. + + Examples + -------- + >>> np.fft.fft([0, 1, 0, 0]) + array([ 1.+0.j, 0.-1.j, -1.+0.j, 0.+1.j]) + >>> np.fft.rfft([0, 1, 0, 0]) + array([ 1.+0.j, 0.-1.j, -1.+0.j]) + + Notice how the final element of the `fft` output is the complex conjugate + of the second element, for real input. For `rfft`, this symmetry is + exploited to compute only the non-negative frequency terms. + + """ + + a = asarray(a).astype(float) + return _raw_fft(a, n, axis, fftpack.rffti, fftpack.rfftf, _real_fft_cache) + + +def irfft(a, n=None, axis=-1): + """ + Compute the inverse of the n-point DFT for real input. + + This function computes the inverse of the one-dimensional *n*-point + discrete Fourier Transform of real input computed by `rfft`. + In other words, ``irfft(rfft(a), len(a)) == a`` to within numerical + accuracy. (See Notes below for why ``len(a)`` is necessary here.) + + The input is expected to be in the form returned by `rfft`, i.e. the + real zero-frequency term followed by the complex positive frequency terms + in order of increasing frequency. Since the discrete Fourier Transform of + real input is Hermitian-symmetric, the negative frequency terms are taken + to be the complex conjugates of the corresponding positive frequency terms. + + Parameters + ---------- + a : array_like + The input array. + n : int, optional + Length of the transformed axis of the output. + For `n` output points, ``n//2+1`` input points are necessary. If the + input is longer than this, it is cropped. If it is shorter than this, + it is padded with zeros. If `n` is not given, it is determined from + the length of the input along the axis specified by `axis`. + axis : int, optional + Axis over which to compute the inverse FFT. If not given, the last + axis is used. + + Returns + ------- + out : ndarray + The truncated or zero-padded input, transformed along the axis + indicated by `axis`, or the last one if `axis` is not specified. + The length of the transformed axis is `n`, or, if `n` is not given, + ``2*(m-1)`` where ``m`` is the length of the transformed axis of the + input. To get an odd number of output points, `n` must be specified. + + Raises + ------ + IndexError + If `axis` is larger than the last axis of `a`. + + See Also + -------- + numpy.fft : For definition of the DFT and conventions used. + rfft : The one-dimensional FFT of real input, of which `irfft` is inverse. + fft : The one-dimensional FFT. + irfft2 : The inverse of the two-dimensional FFT of real input. + irfftn : The inverse of the *n*-dimensional FFT of real input. + + Notes + ----- + Returns the real valued `n`-point inverse discrete Fourier transform + of `a`, where `a` contains the non-negative frequency terms of a + Hermitian-symmetric sequence. `n` is the length of the result, not the + input. + + If you specify an `n` such that `a` must be zero-padded or truncated, the + extra/removed values will be added/removed at high frequencies. One can + thus resample a series to `m` points via Fourier interpolation by: + ``a_resamp = irfft(rfft(a), m)``. + + Examples + -------- + >>> np.fft.ifft([1, -1j, -1, 1j]) + array([ 0.+0.j, 1.+0.j, 0.+0.j, 0.+0.j]) + >>> np.fft.irfft([1, -1j, -1]) + array([ 0., 1., 0., 0.]) + + Notice how the last term in the input to the ordinary `ifft` is the + complex conjugate of the second term, and the output has zero imaginary + part everywhere. When calling `irfft`, the negative frequencies are not + specified, and the output array is purely real. + + """ + + a = asarray(a).astype(complex) + if n is None: + n = (shape(a)[axis] - 1) * 2 + return _raw_fft(a, n, axis, fftpack.rffti, fftpack.rfftb, + _real_fft_cache) / n + + +def hfft(a, n=None, axis=-1): + """ + Compute the FFT of a signal which has Hermitian symmetry (real spectrum). + + Parameters + ---------- + a : array_like + The input array. + n : int, optional + Length of the transformed axis of the output. + For `n` output points, ``n//2+1`` input points are necessary. If the + input is longer than this, it is cropped. If it is shorter than this, + it is padded with zeros. If `n` is not given, it is determined from + the length of the input along the axis specified by `axis`. + axis : int, optional + Axis over which to compute the FFT. If not given, the last + axis is used. + + Returns + ------- + out : ndarray + The truncated or zero-padded input, transformed along the axis + indicated by `axis`, or the last one if `axis` is not specified. + The length of the transformed axis is `n`, or, if `n` is not given, + ``2*(m-1)`` where ``m`` is the length of the transformed axis of the + input. To get an odd number of output points, `n` must be specified. + + Raises + ------ + IndexError + If `axis` is larger than the last axis of `a`. + + See also + -------- + rfft : Compute the one-dimensional FFT for real input. + ihfft : The inverse of `hfft`. + + Notes + ----- + `hfft`/`ihfft` are a pair analogous to `rfft`/`irfft`, but for the + opposite case: here the signal has Hermitian symmetry in the time domain + and is real in the frequency domain. So here it's `hfft` for which + you must supply the length of the result if it is to be odd: + ``ihfft(hfft(a), len(a)) == a``, within numerical accuracy. + + Examples + -------- + >>> signal = np.array([1, 2, 3, 4, 3, 2]) + >>> np.fft.fft(signal) + array([ 15.+0.j, -4.+0.j, 0.+0.j, -1.-0.j, 0.+0.j, -4.+0.j]) + >>> np.fft.hfft(signal[:4]) # Input first half of signal + array([ 15., -4., 0., -1., 0., -4.]) + >>> np.fft.hfft(signal, 6) # Input entire signal and truncate + array([ 15., -4., 0., -1., 0., -4.]) + + + >>> signal = np.array([[1, 1.j], [-1.j, 2]]) + >>> np.conj(signal.T) - signal # check Hermitian symmetry + array([[ 0.-0.j, 0.+0.j], + [ 0.+0.j, 0.-0.j]]) + >>> freq_spectrum = np.fft.hfft(signal) + >>> freq_spectrum + array([[ 1., 1.], + [ 2., -2.]]) + + """ + + a = asarray(a).astype(complex) + if n is None: + n = (shape(a)[axis] - 1) * 2 + return irfft(conjugate(a), n, axis) * n + + +def ihfft(a, n=None, axis=-1): + """ + Compute the inverse FFT of a signal which has Hermitian symmetry. + + Parameters + ---------- + a : array_like + Input array. + n : int, optional + Length of the inverse FFT. + Number of points along transformation axis in the input to use. + If `n` is smaller than the length of the input, the input is cropped. + If it is larger, the input is padded with zeros. If `n` is not given, + the length of the input along the axis specified by `axis` is used. + axis : int, optional + Axis over which to compute the inverse FFT. If not given, the last + axis is used. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axis + indicated by `axis`, or the last one if `axis` is not specified. + If `n` is even, the length of the transformed axis is ``(n/2)+1``. + If `n` is odd, the length is ``(n+1)/2``. + + See also + -------- + hfft, irfft + + Notes + ----- + `hfft`/`ihfft` are a pair analogous to `rfft`/`irfft`, but for the + opposite case: here the signal has Hermitian symmetry in the time domain + and is real in the frequency domain. So here it's `hfft` for which + you must supply the length of the result if it is to be odd: + ``ihfft(hfft(a), len(a)) == a``, within numerical accuracy. + + Examples + -------- + >>> spectrum = np.array([ 15, -4, 0, -1, 0, -4]) + >>> np.fft.ifft(spectrum) + array([ 1.+0.j, 2.-0.j, 3.+0.j, 4.+0.j, 3.+0.j, 2.-0.j]) + >>> np.fft.ihfft(spectrum) + array([ 1.-0.j, 2.-0.j, 3.-0.j, 4.-0.j]) + + """ + + a = asarray(a).astype(float) + if n is None: + n = shape(a)[axis] + return conjugate(rfft(a, n, axis))/n + + +def _cook_nd_args(a, s=None, axes=None, invreal=0): + if s is None: + shapeless = 1 + if axes is None: + s = list(a.shape) + else: + s = take(a.shape, axes) + else: + shapeless = 0 + s = list(s) + if axes is None: + axes = list(range(-len(s), 0)) + if len(s) != len(axes): + raise ValueError("Shape and axes have different lengths.") + if invreal and shapeless: + s[-1] = (a.shape[axes[-1]] - 1) * 2 + return s, axes + + +def _raw_fftnd(a, s=None, axes=None, function=fft): + a = asarray(a) + s, axes = _cook_nd_args(a, s, axes) + itl = list(range(len(axes))) + itl.reverse() + for ii in itl: + a = function(a, n=s[ii], axis=axes[ii]) + return a + + +def fftn(a, s=None, axes=None): + """ + Compute the N-dimensional discrete Fourier Transform. + + This function computes the *N*-dimensional discrete Fourier Transform over + any number of axes in an *M*-dimensional array by means of the Fast Fourier + Transform (FFT). + + Parameters + ---------- + a : array_like + Input array, can be complex. + s : sequence of ints, optional + Shape (length of each transformed axis) of the output + (`s[0]` refers to axis 0, `s[1]` to axis 1, etc.). + This corresponds to `n` for `fft(x, n)`. + Along any axis, if the given shape is smaller than that of the input, + the input is cropped. If it is larger, the input is padded with zeros. + if `s` is not given, the shape of the input along the axes specified + by `axes` is used. + axes : sequence of ints, optional + Axes over which to compute the FFT. If not given, the last ``len(s)`` + axes are used, or all axes if `s` is also not specified. + Repeated indices in `axes` means that the transform over that axis is + performed multiple times. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axes + indicated by `axes`, or by a combination of `s` and `a`, + as explained in the parameters section above. + + Raises + ------ + ValueError + If `s` and `axes` have different length. + IndexError + If an element of `axes` is larger than than the number of axes of `a`. + + See Also + -------- + numpy.fft : Overall view of discrete Fourier transforms, with definitions + and conventions used. + ifftn : The inverse of `fftn`, the inverse *n*-dimensional FFT. + fft : The one-dimensional FFT, with definitions and conventions used. + rfftn : The *n*-dimensional FFT of real input. + fft2 : The two-dimensional FFT. + fftshift : Shifts zero-frequency terms to centre of array + + Notes + ----- + The output, analogously to `fft`, contains the term for zero frequency in + the low-order corner of all axes, the positive frequency terms in the + first half of all axes, the term for the Nyquist frequency in the middle + of all axes and the negative frequency terms in the second half of all + axes, in order of decreasingly negative frequency. + + See `numpy.fft` for details, definitions and conventions used. + + Examples + -------- + >>> a = np.mgrid[:3, :3, :3][0] + >>> np.fft.fftn(a, axes=(1, 2)) + array([[[ 0.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j]], + [[ 9.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j]], + [[ 18.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j]]]) + >>> np.fft.fftn(a, (2, 2), axes=(0, 1)) + array([[[ 2.+0.j, 2.+0.j, 2.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j]], + [[-2.+0.j, -2.+0.j, -2.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j]]]) + + >>> import matplotlib.pyplot as plt + >>> [X, Y] = np.meshgrid(2 * np.pi * np.arange(200) / 12, + ... 2 * np.pi * np.arange(200) / 34) + >>> S = np.sin(X) + np.cos(Y) + np.random.uniform(0, 1, X.shape) + >>> FS = np.fft.fftn(S) + >>> plt.imshow(np.log(np.abs(np.fft.fftshift(FS))**2)) + <matplotlib.image.AxesImage object at 0x...> + >>> plt.show() + + """ + + return _raw_fftnd(a, s, axes, fft) + +def ifftn(a, s=None, axes=None): + """ + Compute the N-dimensional inverse discrete Fourier Transform. + + This function computes the inverse of the N-dimensional discrete + Fourier Transform over any number of axes in an M-dimensional array by + means of the Fast Fourier Transform (FFT). In other words, + ``ifftn(fftn(a)) == a`` to within numerical accuracy. + For a description of the definitions and conventions used, see `numpy.fft`. + + The input, analogously to `ifft`, should be ordered in the same way as is + returned by `fftn`, i.e. it should have the term for zero frequency + in all axes in the low-order corner, the positive frequency terms in the + first half of all axes, the term for the Nyquist frequency in the middle + of all axes and the negative frequency terms in the second half of all + axes, in order of decreasingly negative frequency. + + Parameters + ---------- + a : array_like + Input array, can be complex. + s : sequence of ints, optional + Shape (length of each transformed axis) of the output + (``s[0]`` refers to axis 0, ``s[1]`` to axis 1, etc.). + This corresponds to ``n`` for ``ifft(x, n)``. + Along any axis, if the given shape is smaller than that of the input, + the input is cropped. If it is larger, the input is padded with zeros. + if `s` is not given, the shape of the input along the axes specified + by `axes` is used. See notes for issue on `ifft` zero padding. + axes : sequence of ints, optional + Axes over which to compute the IFFT. If not given, the last ``len(s)`` + axes are used, or all axes if `s` is also not specified. + Repeated indices in `axes` means that the inverse transform over that + axis is performed multiple times. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axes + indicated by `axes`, or by a combination of `s` or `a`, + as explained in the parameters section above. + + Raises + ------ + ValueError + If `s` and `axes` have different length. + IndexError + If an element of `axes` is larger than than the number of axes of `a`. + + See Also + -------- + numpy.fft : Overall view of discrete Fourier transforms, with definitions + and conventions used. + fftn : The forward *n*-dimensional FFT, of which `ifftn` is the inverse. + ifft : The one-dimensional inverse FFT. + ifft2 : The two-dimensional inverse FFT. + ifftshift : Undoes `fftshift`, shifts zero-frequency terms to beginning + of array. + + Notes + ----- + See `numpy.fft` for definitions and conventions used. + + Zero-padding, analogously with `ifft`, is performed by appending zeros to + the input along the specified dimension. Although this is the common + approach, it might lead to surprising results. If another form of zero + padding is desired, it must be performed before `ifftn` is called. + + Examples + -------- + >>> a = np.eye(4) + >>> np.fft.ifftn(np.fft.fftn(a, axes=(0,)), axes=(1,)) + array([[ 1.+0.j, 0.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 1.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 1.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j, 1.+0.j]]) + + + Create and plot an image with band-limited frequency content: + + >>> import matplotlib.pyplot as plt + >>> n = np.zeros((200,200), dtype=complex) + >>> n[60:80, 20:40] = np.exp(1j*np.random.uniform(0, 2*np.pi, (20, 20))) + >>> im = np.fft.ifftn(n).real + >>> plt.imshow(im) + <matplotlib.image.AxesImage object at 0x...> + >>> plt.show() + + """ + + return _raw_fftnd(a, s, axes, ifft) + + +def fft2(a, s=None, axes=(-2, -1)): + """ + Compute the 2-dimensional discrete Fourier Transform + + This function computes the *n*-dimensional discrete Fourier Transform + over any axes in an *M*-dimensional array by means of the + Fast Fourier Transform (FFT). By default, the transform is computed over + the last two axes of the input array, i.e., a 2-dimensional FFT. + + Parameters + ---------- + a : array_like + Input array, can be complex + s : sequence of ints, optional + Shape (length of each transformed axis) of the output + (`s[0]` refers to axis 0, `s[1]` to axis 1, etc.). + This corresponds to `n` for `fft(x, n)`. + Along each axis, if the given shape is smaller than that of the input, + the input is cropped. If it is larger, the input is padded with zeros. + if `s` is not given, the shape of the input along the axes specified + by `axes` is used. + axes : sequence of ints, optional + Axes over which to compute the FFT. If not given, the last two + axes are used. A repeated index in `axes` means the transform over + that axis is performed multiple times. A one-element sequence means + that a one-dimensional FFT is performed. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axes + indicated by `axes`, or the last two axes if `axes` is not given. + + Raises + ------ + ValueError + If `s` and `axes` have different length, or `axes` not given and + ``len(s) != 2``. + IndexError + If an element of `axes` is larger than than the number of axes of `a`. + + See Also + -------- + numpy.fft : Overall view of discrete Fourier transforms, with definitions + and conventions used. + ifft2 : The inverse two-dimensional FFT. + fft : The one-dimensional FFT. + fftn : The *n*-dimensional FFT. + fftshift : Shifts zero-frequency terms to the center of the array. + For two-dimensional input, swaps first and third quadrants, and second + and fourth quadrants. + + Notes + ----- + `fft2` is just `fftn` with a different default for `axes`. + + The output, analogously to `fft`, contains the term for zero frequency in + the low-order corner of the transformed axes, the positive frequency terms + in the first half of these axes, the term for the Nyquist frequency in the + middle of the axes and the negative frequency terms in the second half of + the axes, in order of decreasingly negative frequency. + + See `fftn` for details and a plotting example, and `numpy.fft` for + definitions and conventions used. + + + Examples + -------- + >>> a = np.mgrid[:5, :5][0] + >>> np.fft.fft2(a) + array([[ 50.0 +0.j , 0.0 +0.j , 0.0 +0.j , + 0.0 +0.j , 0.0 +0.j ], + [-12.5+17.20477401j, 0.0 +0.j , 0.0 +0.j , + 0.0 +0.j , 0.0 +0.j ], + [-12.5 +4.0614962j , 0.0 +0.j , 0.0 +0.j , + 0.0 +0.j , 0.0 +0.j ], + [-12.5 -4.0614962j , 0.0 +0.j , 0.0 +0.j , + 0.0 +0.j , 0.0 +0.j ], + [-12.5-17.20477401j, 0.0 +0.j , 0.0 +0.j , + 0.0 +0.j , 0.0 +0.j ]]) + + """ + + return _raw_fftnd(a, s, axes, fft) + + +def ifft2(a, s=None, axes=(-2, -1)): + """ + Compute the 2-dimensional inverse discrete Fourier Transform. + + This function computes the inverse of the 2-dimensional discrete Fourier + Transform over any number of axes in an M-dimensional array by means of + the Fast Fourier Transform (FFT). In other words, ``ifft2(fft2(a)) == a`` + to within numerical accuracy. By default, the inverse transform is + computed over the last two axes of the input array. + + The input, analogously to `ifft`, should be ordered in the same way as is + returned by `fft2`, i.e. it should have the term for zero frequency + in the low-order corner of the two axes, the positive frequency terms in + the first half of these axes, the term for the Nyquist frequency in the + middle of the axes and the negative frequency terms in the second half of + both axes, in order of decreasingly negative frequency. + + Parameters + ---------- + a : array_like + Input array, can be complex. + s : sequence of ints, optional + Shape (length of each axis) of the output (``s[0]`` refers to axis 0, + ``s[1]`` to axis 1, etc.). This corresponds to `n` for ``ifft(x, n)``. + Along each axis, if the given shape is smaller than that of the input, + the input is cropped. If it is larger, the input is padded with zeros. + if `s` is not given, the shape of the input along the axes specified + by `axes` is used. See notes for issue on `ifft` zero padding. + axes : sequence of ints, optional + Axes over which to compute the FFT. If not given, the last two + axes are used. A repeated index in `axes` means the transform over + that axis is performed multiple times. A one-element sequence means + that a one-dimensional FFT is performed. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axes + indicated by `axes`, or the last two axes if `axes` is not given. + + Raises + ------ + ValueError + If `s` and `axes` have different length, or `axes` not given and + ``len(s) != 2``. + IndexError + If an element of `axes` is larger than than the number of axes of `a`. + + See Also + -------- + numpy.fft : Overall view of discrete Fourier transforms, with definitions + and conventions used. + fft2 : The forward 2-dimensional FFT, of which `ifft2` is the inverse. + ifftn : The inverse of the *n*-dimensional FFT. + fft : The one-dimensional FFT. + ifft : The one-dimensional inverse FFT. + + Notes + ----- + `ifft2` is just `ifftn` with a different default for `axes`. + + See `ifftn` for details and a plotting example, and `numpy.fft` for + definition and conventions used. + + Zero-padding, analogously with `ifft`, is performed by appending zeros to + the input along the specified dimension. Although this is the common + approach, it might lead to surprising results. If another form of zero + padding is desired, it must be performed before `ifft2` is called. + + Examples + -------- + >>> a = 4 * np.eye(4) + >>> np.fft.ifft2(a) + array([[ 1.+0.j, 0.+0.j, 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j, 0.+0.j, 1.+0.j], + [ 0.+0.j, 0.+0.j, 1.+0.j, 0.+0.j], + [ 0.+0.j, 1.+0.j, 0.+0.j, 0.+0.j]]) + + """ + + return _raw_fftnd(a, s, axes, ifft) + + +def rfftn(a, s=None, axes=None): + """ + Compute the N-dimensional discrete Fourier Transform for real input. + + This function computes the N-dimensional discrete Fourier Transform over + any number of axes in an M-dimensional real array by means of the Fast + Fourier Transform (FFT). By default, all axes are transformed, with the + real transform performed over the last axis, while the remaining + transforms are complex. + + Parameters + ---------- + a : array_like + Input array, taken to be real. + s : sequence of ints, optional + Shape (length along each transformed axis) to use from the input. + (``s[0]`` refers to axis 0, ``s[1]`` to axis 1, etc.). + The final element of `s` corresponds to `n` for ``rfft(x, n)``, while + for the remaining axes, it corresponds to `n` for ``fft(x, n)``. + Along any axis, if the given shape is smaller than that of the input, + the input is cropped. If it is larger, the input is padded with zeros. + if `s` is not given, the shape of the input along the axes specified + by `axes` is used. + axes : sequence of ints, optional + Axes over which to compute the FFT. If not given, the last ``len(s)`` + axes are used, or all axes if `s` is also not specified. + + Returns + ------- + out : complex ndarray + The truncated or zero-padded input, transformed along the axes + indicated by `axes`, or by a combination of `s` and `a`, + as explained in the parameters section above. + The length of the last axis transformed will be ``s[-1]//2+1``, + while the remaining transformed axes will have lengths according to + `s`, or unchanged from the input. + + Raises + ------ + ValueError + If `s` and `axes` have different length. + IndexError + If an element of `axes` is larger than than the number of axes of `a`. + + See Also + -------- + irfftn : The inverse of `rfftn`, i.e. the inverse of the n-dimensional FFT + of real input. + fft : The one-dimensional FFT, with definitions and conventions used. + rfft : The one-dimensional FFT of real input. + fftn : The n-dimensional FFT. + rfft2 : The two-dimensional FFT of real input. + + Notes + ----- + The transform for real input is performed over the last transformation + axis, as by `rfft`, then the transform over the remaining axes is + performed as by `fftn`. The order of the output is as for `rfft` for the + final transformation axis, and as for `fftn` for the remaining + transformation axes. + + See `fft` for details, definitions and conventions used. + + Examples + -------- + >>> a = np.ones((2, 2, 2)) + >>> np.fft.rfftn(a) + array([[[ 8.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j]], + [[ 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j]]]) + + >>> np.fft.rfftn(a, axes=(2, 0)) + array([[[ 4.+0.j, 0.+0.j], + [ 4.+0.j, 0.+0.j]], + [[ 0.+0.j, 0.+0.j], + [ 0.+0.j, 0.+0.j]]]) + + """ + + a = asarray(a).astype(float) + s, axes = _cook_nd_args(a, s, axes) + a = rfft(a, s[-1], axes[-1]) + for ii in range(len(axes)-1): + a = fft(a, s[ii], axes[ii]) + return a + +def rfft2(a, s=None, axes=(-2, -1)): + """ + Compute the 2-dimensional FFT of a real array. + + Parameters + ---------- + a : array + Input array, taken to be real. + s : sequence of ints, optional + Shape of the FFT. + axes : sequence of ints, optional + Axes over which to compute the FFT. + + Returns + ------- + out : ndarray + The result of the real 2-D FFT. + + See Also + -------- + rfftn : Compute the N-dimensional discrete Fourier Transform for real + input. + + Notes + ----- + This is really just `rfftn` with different default behavior. + For more details see `rfftn`. + + """ + + return rfftn(a, s, axes) + +def irfftn(a, s=None, axes=None): + """ + Compute the inverse of the N-dimensional FFT of real input. + + This function computes the inverse of the N-dimensional discrete + Fourier Transform for real input over any number of axes in an + M-dimensional array by means of the Fast Fourier Transform (FFT). In + other words, ``irfftn(rfftn(a), a.shape) == a`` to within numerical + accuracy. (The ``a.shape`` is necessary like ``len(a)`` is for `irfft`, + and for the same reason.) + + The input should be ordered in the same way as is returned by `rfftn`, + i.e. as for `irfft` for the final transformation axis, and as for `ifftn` + along all the other axes. + + Parameters + ---------- + a : array_like + Input array. + s : sequence of ints, optional + Shape (length of each transformed axis) of the output + (``s[0]`` refers to axis 0, ``s[1]`` to axis 1, etc.). `s` is also the + number of input points used along this axis, except for the last axis, + where ``s[-1]//2+1`` points of the input are used. + Along any axis, if the shape indicated by `s` is smaller than that of + the input, the input is cropped. If it is larger, the input is padded + with zeros. If `s` is not given, the shape of the input along the + axes specified by `axes` is used. + axes : sequence of ints, optional + Axes over which to compute the inverse FFT. If not given, the last + `len(s)` axes are used, or all axes if `s` is also not specified. + Repeated indices in `axes` means that the inverse transform over that + axis is performed multiple times. + + Returns + ------- + out : ndarray + The truncated or zero-padded input, transformed along the axes + indicated by `axes`, or by a combination of `s` or `a`, + as explained in the parameters section above. + The length of each transformed axis is as given by the corresponding + element of `s`, or the length of the input in every axis except for the + last one if `s` is not given. In the final transformed axis the length + of the output when `s` is not given is ``2*(m-1)`` where ``m`` is the + length of the final transformed axis of the input. To get an odd + number of output points in the final axis, `s` must be specified. + + Raises + ------ + ValueError + If `s` and `axes` have different length. + IndexError + If an element of `axes` is larger than than the number of axes of `a`. + + See Also + -------- + rfftn : The forward n-dimensional FFT of real input, + of which `ifftn` is the inverse. + fft : The one-dimensional FFT, with definitions and conventions used. + irfft : The inverse of the one-dimensional FFT of real input. + irfft2 : The inverse of the two-dimensional FFT of real input. + + Notes + ----- + See `fft` for definitions and conventions used. + + See `rfft` for definitions and conventions used for real input. + + Examples + -------- + >>> a = np.zeros((3, 2, 2)) + >>> a[0, 0, 0] = 3 * 2 * 2 + >>> np.fft.irfftn(a) + array([[[ 1., 1.], + [ 1., 1.]], + [[ 1., 1.], + [ 1., 1.]], + [[ 1., 1.], + [ 1., 1.]]]) + + """ + + a = asarray(a).astype(complex) + s, axes = _cook_nd_args(a, s, axes, invreal=1) + for ii in range(len(axes)-1): + a = ifft(a, s[ii], axes[ii]) + a = irfft(a, s[-1], axes[-1]) + return a + +def irfft2(a, s=None, axes=(-2, -1)): + """ + Compute the 2-dimensional inverse FFT of a real array. + + Parameters + ---------- + a : array_like + The input array + s : sequence of ints, optional + Shape of the inverse FFT. + axes : sequence of ints, optional + The axes over which to compute the inverse fft. + Default is the last two axes. + + Returns + ------- + out : ndarray + The result of the inverse real 2-D FFT. + + See Also + -------- + irfftn : Compute the inverse of the N-dimensional FFT of real input. + + Notes + ----- + This is really `irfftn` with different defaults. + For more details see `irfftn`. + + """ + + return irfftn(a, s, axes)