abs — Absolute value and complex magnitude for scalars and arrays in MATLAB and RunMat.

y = abs(x) returns absolute values for real inputs and magnitudes for floating complex inputs. For arrays, abs is applied element-wise and preserves the input shape. All eight integer classes preserve their input class and use saturating arithmetic at the signed minimum.

Syntax

Y = abs(X)

Inputs

Returns

Errors

How abs works

• Real scalars, vectors, matrices, and N-D tensors are mapped to their element-wise absolute values.
• Complex single and double inputs return the magnitude sqrt(real(x).^2 + imag(x).^2) in the corresponding real floating class; typed complex integer inputs are rejected.
• Integer scalars and full arrays preserve exact class and shape. Unsigned values are unchanged, signed values are negated, and abs(intmin(class)) saturates to intmax(class).
• Sparse single and double inputs retain their CSC structure and native class. Exact sparse integer storage is available only in RunMat compatibility mode.
• Logical inputs are a declared RunMat-only extension and are promoted to doubles (true → 1.0, false → 0.0).
• Character arrays are a declared RunMat-only extension and are converted to double code-point magnitudes.
• String arrays are not supported and raise an error.
• RunMat does not yet implement the documented duration, table, or timetable overloads.
• NaN values remain NaN; the function does not change IEEE NaN propagation rules.

Does RunMat run abs on the GPU?

Hook available: The absolute value is computed directly on the device with no host transfers.

Hook missing or unsupported dtype: RunMat gathers through authoritative native storage, performs the CPU absolute value logic, and restores the result to the input handle's owning provider. Integer fallback preserves exact class, including 64-bit values.

When a provider supports complex-interleaved storage, abs computes magnitudes on the device and returns a real GPU tensor with the original shape.

GPU memory and residency

You usually do not need to call gpuArray explicitly. RunMat's fusion planner and Accelerate layer track residency automatically, keeping tensors on the GPU whenever device execution is beneficial. Explicit gpuArray/gather calls remain available for MATLAB compatibility or when you need deterministic residency control (e.g., integrating with third-party GPU kernels).

Examples

Getting the absolute value of a scalar

y = abs(-42)

Expected output:

y = 42

Taking the absolute value of a vector

v = [-2 -1 0 1 2];
result = abs(v)

Expected output:

result = [2 1 0 1 2]

Measuring complex magnitudes

z = [3+4i, 1-1i];
magnitudes = abs(z)

Expected output:

magnitudes = [5 1.4142]

Working with matrices on an accelerator

G = randn(2048, 2048, "gpuArray");
positive = abs(G)

Computing magnitudes of logical values

mask = logical([0 1 0; 1 0 1]);
numeric = abs(mask)

Expected output:

numeric = [0 1 0; 1 0 1]

Computing magnitudes of character codes

c = 'ABC';
codes = abs(c)

Expected output:

codes = [65 66 67]

Chaining abs inside fused expressions

x = linspace(-2, 2, 5);
y = abs(x) + x.^2

Using abs with coding agents

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

FAQ

Related Math functions

Open-source implementation

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

• View the source for abs 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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