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CategoryArray: Shape
GPUYes

What does the squeeze function do in MATLAB / RunMat?

squeeze(A) removes singleton (dimension size equal to one) dimensions from A. The result keeps MATLAB's row/column vector semantics—2-D matrices stay 2-D, and higher-rank arrays collapse down until only meaningful axes remain.

How does the squeeze function behave in MATLAB / RunMat?

  • Dimensions greater than two drop all size-one axes. If exactly one dimension remains, the output becomes an N × 1 column vector.
  • Two-dimensional inputs (row/column vectors and matrices) are returned unchanged.
  • Zero-length dimensions are preserved; only length-one axes are removed.
  • Scalar values remain scalars.
  • GPU arrays stay resident on the device where possible; the runtime only gathers when it cannot infer the shape.

squeeze Function GPU Execution Behaviour

When a GPU provider is active, RunMat calls the provider's reshape hook to update tensor metadata without copying data. Providers that do not override reshape fall back to the in-process behaviour, simply updating the handle shape locally. If a handle advertises no shape, RunMat downloads metadata once to infer dimensions before applying squeeze.

Examples of using the squeeze function in MATLAB / RunMat

Removing Singleton Dimensions from a 3-D Matrix

A = reshape(1:12, [1, 3, 4]);
B = squeeze(A);
size(B)

Expected output:

ans = [3 4]

Turning 1x1xN Slices into Column Vectors

T = zeros(1, 1, 5);
T(:, :, 3) = 7;
vec = squeeze(T);
size(vec)

Expected output:

ans = [5 1]

Keeping Row Vectors Unchanged After Squeeze

row = rand(1, 8);
out = squeeze(row);
size(out)

Expected output:

ans = [1 8]

Squeezing Logical Masks from Simulations

mask = false(1, 10, 1, 1);
mask(1, 4, 1, 1) = true;
flat = squeeze(mask);

Expected output:

flat = [0 0 0 1 0 0 0 0 0 0]'

Using Squeeze on GPU-Resident Data

G = gpuArray(rand(1, 64, 1));
H = squeeze(G);
isgpuarray(H)

Expected output:

ans = logical 1

Squeezing String Arrays While Preserving Layout

S = strings(1, 1, 3);
S(1, 1, 1) = "run";
S(1, 1, 2) = "mat";
S(1, 1, 3) = "gpu";
T = squeeze(S);
size(T)

Expected output:

ans = [3 1]

FAQ

Why does squeeze keep 2-D matrices unchanged?

MATLAB treats row and column vectors as 2-D objects. Preserving those dimensions avoids turning row vectors into column vectors or scalars unintentionally.

What happens when every dimension is singleton?

The result becomes a 1 × 1 array. Scalars (e.g., plain doubles) remain scalars.

Does squeeze affect zero-length dimensions?

No. Only size-one dimensions are removed. Zero-length dimensions are preserved exactly.

Can I squeeze character or cell arrays?

Yes. They already store up to two dimensions in RunMat, so squeeze leaves them unchanged but still validates inputs.

How does squeeze interact with GPU tensors?

The runtime updates GPU tensor metadata via the provider's reshape hook. Data stays on the device unless a provider cannot report shape information, in which case RunMat gathers once to infer dimensions.

What if I need to remove a specific dimension?

Use reshape, permute, or indexing to reorganize axes manually before calling squeeze.

Does squeeze change data ordering?

No. It only alters metadata. Element order in memory remains unchanged.

Will squeeze ever increase the number of dimensions?

No. It either returns the same number or fewer. The only exception is padding with a trailing singleton to maintain MATLAB's column-vector convention when exactly one dimension remains.

Is squeeze safe to run before GPU fusion?

Yes. Since it only updates shapes, it integrates cleanly with fusion and does not impede kernel generation.

How do I undo a squeeze?

Use reshape with the original size vector (for example, captured via size(A)) to restore the previous dimension layout.

See Also