ifftshift — Shift centered spectra back to origin ordering in MATLAB and RunMat.

ifftshift(X) circularly shifts data so zero-frequency components move back to origin ordering. Default and dimension-specific shifting behavior follow MATLAB semantics.

Syntax

Y = ifftshift(X)
Y = ifftshift(X, DIM)

Inputs

Returns

Errors

How ifftshift works

• When no dimensions are specified, every axis is shifted by ceil(size(X, dim) / 2).
• Passing a list of dimensions restricts shifting to those axes; zeros and ones are treated as no-ops.
• Odd-length dimensions shift by one additional element compared with fftshift, matching MATLAB's ifftshift parity rules.
• Works for real, complex, logical, and GPU-resident tensors.
• Empty arrays and scalars are returned unchanged.

Does RunMat run ifftshift on the GPU?

RunMat first attempts to execute the shift entirely on the GPU using the provider's circshift hook. If that is unavailable, RunMat gathers the data exactly once, performs the reorder on the host, and uploads the result so downstream computations can continue on the device. Scalars remain on their current device to avoid unnecessary transfers.

GPU memory and residency

You can rely on RunMat's auto-offload to keep FFT data on the GPU. When a provider exposes circshift, ifftshift executes entirely on the device and the result remains GPU-resident. If no provider is registered—or it lacks circshift—RunMat gathers once, applies the host reorder, and uploads the result so the rest of the computation can still run accelerated. You can call gpuArray explicitly when you need MATLAB parity or to enforce a residency boundary.

Examples

Undoing fftshift on an even-length spectrum

x = 0:7;
y = ifftshift(x)

Expected output:

y = [4 5 6 7 0 1 2 3]

Undoing fftshift on an odd-length spectrum

x = 1:5;
y = ifftshift(x)

Expected output:

y = [3 4 5 1 2]

Preparing data for inverse FFT

fx = fft(rand(1, 8));
centered = fftshift(fx);
restored = ifftshift(centered);
signal = ifft(restored)

Shifting only selected dimensions

A = reshape(1:12, 3, 4);
rowsShifted = ifftshift(A, 1);   % shift rows only
colsShifted = ifftshift(A, 2);   % shift columns only

Expected output:

rowsShifted =
     2     5     8    11
     3     6     9    12
     1     4     7    10

colsShifted =
     7    10     1     4
     8    11     2     5
     9    12     3     6

Using ifftshift with gpuArray data

G = gpuArray(0:7);
shifted = ifftshift(G);
host = gather(shifted)

Expected output:

host = [4 5 6 7 0 1 2 3]

Using ifftshift with coding agents

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

FAQ

Related Math functions

Open-source implementation

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

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

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