ifft — Compute inverse discrete Fourier transforms in MATLAB and RunMat.

ifft(X) computes the inverse discrete Fourier transform of X. By default it operates along the first non-singleton dimension, with optional length, dimension, and symmetry forms following MATLAB semantics.

Syntax

Y = ifft(X)
Y = ifft(X, N)
Y = ifft(X, symflag)
Y = ifft(X, N, DIM)
Y = ifft(X, N, symflag)
Y = ifft(X, N, DIM, symflag)

Inputs

Returns

Errors

How ifft works

• ifft(X) transforms along the first dimension whose size is greater than 1.
• ifft(X, N) zero-pads or truncates X to length N before applying the transform.
• ifft(X, N, DIM) applies the transform along dimension DIM.
• ifft(X, [], DIM) keeps the existing length and transforms along dimension DIM.
• ifft(..., 'symmetric') forces the output to be real-valued, mirroring MATLAB's handling of conjugate-symmetric spectra.
• ifft(..., 'nonsymmetric') keeps the default complex result; it is equivalent to omitting the symmetry flag but is accepted for MATLAB compatibility.
• Empty inputs and dimensions larger than the rank of X mirror MATLAB behaviour.

Does RunMat run ifft on the GPU?

RunMat keeps gpuArray inputs on the device long enough to query the active acceleration provider for the ifft_dim hook. When the hook is present, the inverse transform executes on the device, after which RunMat immediately downloads the result to return the standard MATLAB host types. If the provider lacks that hook—or if the requested length is zero—the runtime gathers the data once, evaluates the inverse transform on the CPU via rustfft, and returns a MATLAB-compatible result.

GPU memory and residency

RunMat's auto-offload system keeps tensors on the GPU when profitable, so explicit gpuArray calls are rarely required. They remain available to mirror MATLAB workflows. When the provider lacks an inverse FFT hook, RunMat automatically gathers once, evaluates the transform on the host, and returns the result, so manual residency management is unnecessary.

Examples

Reconstructing a time-domain signal from FFT bins

Y = [10  -2+2i  -2  -2-2i];
x = ifft(Y)

Expected output:

x =
  Columns 1 through 4
       1     2     3     4

Computing ifft along a specific dimension

F = [10  14  18;
     -3+3i  -3+3i  -3+3i];
X = ifft(F, [], 1)

Zero-padding the inverse transform

F = [4 0 0 0];
x = ifft(F, 8)

Enforcing a real result with 'symmetric'

F = fft([1 2 3 4]);
x = ifft(F, 'symmetric')

Running ifft on gpuArray inputs

G = gpuArray(fft([1 0 0 0]));
X = ifft(G);
result = gather(X)

Using ifft with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how ifft changes the result.

FAQ

Related Math functions

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how ifft is executed, line by line, in Rust.

• View the source for ifft in Rust on GitHub
• Learn how the RunMat runtime works
• Found a bug? Open an issue with a minimal reproduction.

About RunMat

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