Fft.md

FFT — NVMathNet.Fft

Memory layout

Unlike the BLAS-style modules, FFT shapes are row-major (cuFFT convention): in a shape such as [batch, n] the last axis is contiguous in memory. axes selects the dimensions to transform; they must be ascending, contiguous and include the first or last dimension. Transforming a leading axis (for example shape [8, 3], axes [0]) uses a strided layout. For R2C the shape is the real input; for C2R it is the real output, and the half-spectrum has n/2 + 1 bins along the last transformed axis.

Enums

enum FftDirection { Forward = -1, Inverse = 1 }
enum FftType { C2C, R2C, C2R }
enum LastAxisParity { Even, Odd }
enum FftNormalization { None, Backward, Forward, Orthonormal }

FftOptions

Property	Type	Default	Description
FftType	FftType?	null (auto)	Transform type.
InPlace	bool	false	Execute in-place.
LastAxisParity	LastAxisParity	Even	Parity of the last axis for R2C/C2R.
DeviceId	int	0	GPU device index.
Blocking	bool	false	Synchronise after execution.
Normalization	FftNormalization	None	Output scaling: None (cuFFT behaviour), Backward (1/N on inverse), Forward (1/N on forward), Orthonormal (1/√N on both). R2C counts as forward and C2R as inverse.

Fft (class)

Stateful cuFFT plan wrapper. Implements IAsyncDisposable, IDisposable.

Member	Description
Fft(long[] shape, int[]? axes = null, FftOptions? options = null, CudaStream? stream = null, bool doublePrecision = false)	Creates a plan descriptor. axes selects which dimensions to transform (null = all); they must be ascending, contiguous and include the first or last dimension (negative values allowed). Batched trailing- and leading-axis layouts are supported.
Task PlanAsync(CancellationToken ct = default)	Builds the cuFFT plan.
void Plan()	Synchronous plan creation.
Task ExecuteAsync(FftDirection direction = Forward, CancellationToken ct = default)	Executes the transform.
void Execute(FftDirection direction = Forward)	Synchronous execution.
void ResetOperand(nint inputPtr, nint outputPtr)	Changes data pointers without replanning.
Task SynchronizeAsync(CancellationToken ct = default)	Synchronises the stream.

Static Helpers

Method	Description
static Task<DeviceBuffer<Complex>> FftAsync(...)	One-shot forward C2C FFT. Returns new output buffer.
static Task<DeviceBuffer<Complex>> IFftAsync(...)	One-shot inverse C2C FFT.
static Task<DeviceBuffer<Complex>> RFftAsync(DeviceBuffer<double> input, long[] shape, ...)	Double-precision real-to-complex FFT. Output length = n/2+1 along the last axis.
static Task<DeviceBuffer<float>> RFftAsync(DeviceBuffer<float> input, long[] shape, ...)	Single-precision real-to-complex FFT. .NET has no single-precision complex type, so the result is interleaved (re, im) floats (2 * (n/2+1) per row).
static Task<DeviceBuffer<double>> IRFftAsync(DeviceBuffer<Complex> input, long[] outputShape, ...)	Double-precision complex-to-real inverse FFT.
static Task<DeviceBuffer<float>> IRFftAsync(DeviceBuffer<float> input, long[] outputShape, ...)	Single-precision complex-to-real inverse FFT; input is interleaved (re, im) floats.