isinf — Test infinite values element-wise in MATLAB and RunMat.

mask = isinf(x) returns a logical mask indicating which elements are +Inf or -Inf. Output shape and type handling follow MATLAB semantics.

Syntax

tf = isinf(A)

Inputs

Returns

Errors

How isinf works

• Numeric scalars return a logical scalar (true/false).
• Numeric arrays return a logical array of the same size, with true wherever the corresponding element is +Inf or -Inf.
• Complex inputs report true when either the real or the imaginary component is infinite.
• Logical inputs return false because logical values (0 or 1) are finite by construction.
• Character arrays return logical arrays of zeros (characters map to finite code points).
• String arrays return logical arrays of zeros, mirroring MATLAB behavior.
• string scalars (string objects) return a logical scalar false.
• When the input is a gpuArray, RunMat keeps the computation on the device if the active acceleration provider implements the logical_isinf hook; otherwise the runtime gathers the data back to the host automatically.

Does RunMat run isinf on the GPU?

When RunMat Accelerate is active, isinf looks for the provider hook logical_isinf. Providers that implement the hook execute the infinity test entirely on the GPU, producing a logical gpuArray result without any host transfers. If the hook is absent, RunMat gathers the input tensor back to the CPU, computes the mask on the host, and returns a regular logical array so the builtin always succeeds.

GPU memory and residency

You usually do not need to call gpuArray explicitly. RunMat's auto-offload planner keeps tensors on the GPU across fused expressions when that improves performance. You can still seed residency manually with gpuArray for compatibility with MATLAB scripts or when you want fine-grained control over data movement.

Examples

Checking if a scalar is infinite

result = isinf(1/0)

Expected output:

result =
     1

Detecting infinities after division by zero

A = [1 0; 2 0];
quot = 1 ./ A;
mask = isinf(quot)

Expected output:

mask =
  2×2 logical array
     0     1
     0     1

Flagging infinite components of a complex array

Z = [Inf+0i 1-Inf*1i 2+3i];
mask = isinf(Z)

Expected output:

mask =
  1×3 logical array
     1     1     0

Applying isinf to character data

chars = ['R' 'u' 'n'];
mask = isinf(chars)

Expected output:

mask =
  1×3 logical array
     0     0     0

Running isinf directly on the GPU

G = gpuArray([1 -Inf Inf]);
mask_gpu = isinf(G);
mask = gather(mask_gpu)

Expected output:

mask =
  1×3 logical array
     0     1     1

Using isinf with coding agents

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

FAQ

Related Logical functions

Open-source implementation

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

• View the source for isinf 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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