File fft.hxx#

FFT routines

This file is part of BOUT++.

BOUT++ is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

BOUT++ is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with BOUT++. If not, see http://www.gnu.org/licenses/.

Functions

BOUT_ENUM_CLASS(FFT_MEASUREMENT_FLAG, estimate, measure, exhaustive)#

inline void rfft(const BoutReal *in, int length, dcomplex *out)#

inline void irfft(const dcomplex *in, int length, BoutReal *out)#

inline void DST(const BoutReal *in, int length, dcomplex *out)#

inline void DST_rev(dcomplex *in, int length, BoutReal *out)#

namespace bout

Provides access to the Hypre library, handling initialisation and finalisation.

Usage

#include <bout/hyprelib.hxx>

class MyClass { public:

private: HypreLib lib; };

This will then automatically initialise Hypre the first time an object is created, and finalise it when the last object is destroyed.

Contact: Ben Dudson, bd512@york.ac.uk

This file is part of BOUT++.

You should have received a copy of the GNU Lesser General Public License along with BOUT++. If not, see http://www.gnu.org/licenses/.

Explicit inversion of a 3x3 matrix a

If the matrix is singular (ill conditioned), the determinant is return. Otherwise, an empty std::optional is return

SNB model

namespace fft#

Functions

void rfft(const BoutReal *in, int length, dcomplex *out)#

Returns the fft of a real signal using fftw_forward

The fftw_forward returns out_k = sum_{j=0}^(length-1) in_j*exp(-2*pi*j*k*sqrt(-1)/length)

Thus, out_k must be divided by ‘length’ in order for DFT[IDFT[in]] = in where IDFT is the inverse fourier transform. See the the fftw user manual for details.

Parameters:

in – [in] Pointer to the 1D array to take the fourier transform of
length – [in] Number of points in the input array
out – [out] Pointer to the complex 1D array which is the FFT of in

void irfft(const dcomplex *in, int length, BoutReal *out)#

Take the inverse fft of signal where the outputs are only reals.

This is done through a call to fftw_plan_dft_c2r_1d which is calling fftw_backwards.

That is out_k = sum_{j=0}^(length-1) in_j*exp(2*pi*j*k*sqrt(-1)/length)

See the the fftw user manual for details.

Parameters:

in – [in] Pointer to the 1D array to take the inverse fourier transform of
length – [in] Number of points in the input array
out – [out] Pointer to the complex 1D array which is IFFTed

void DST(const BoutReal *in, int length, dcomplex *out)#

Discrete Sine Transform

in and out arrays must both be of the same length

void DST_rev(dcomplex *in, int length, BoutReal *out)#

Inverse Discrete Sine Transform

in and out arrays must both be of the same length