What does the `gpuDevice` function do in MATLAB / RunMat?

info = gpuDevice() queries the active accelerator provider and returns a MATLAB struct that describes the GPU (or GPU-like backend) that RunMat is currently using. The struct mirrors MathWorks MATLAB's gpuDevice metadata, exposing identifiers, vendor information, memory hints, and precision support so you can adapt algorithms at runtime.

The returned struct contains a subset of these fields (providers may omit ones they cannot populate):

device_id — zero-based identifier reported by the provider.
index — MATLAB-style one-based index derived from device_id.
name — human-readable adapter name.
vendor — provider-reported vendor or implementation name.
backend — backend identifier such as inprocess or Vulkan (optional).
memory_bytes — total device memory in bytes when known (optional).
precision — string describing the scalar precision used for kernels ("double" or "single").
supports_double — logical flag that is true when double precision kernels are available.

The builtin raises gpuDevice: no acceleration provider registered when no provider is active.

How does the `gpuDevice` function behave in MATLAB / RunMat?

Requires an acceleration provider that implements RunMat Accelerate's AccelProvider trait.
Returns a struct so you can access fields with dot notation: gpuDevice().name.
Does not mutate GPU state or enqueue kernels—it is safe to call frequently.
Accepts a scalar device index; gpuDevice(1) returns the active provider, while any other index raises the MATLAB-style error gpuDevice: GPU device with index N not available.
Requests to reset the provider using gpuDevice('reset') or gpuDevice([]) currently raise gpuDevice: reset is not supported by the active provider.
Hooks into gpuInfo so the string-form summary stays in sync with the struct fields.

GPU residency in RunMat (Do I need `gpuArray`?)

gpuDevice purely reports metadata and does not change residency. Arrays remain on the GPU or CPU exactly as they were prior to the call. Use gpuArray, gather, and the planner-controlled automatic residency features to move data as needed.

Examples of using the `gpuDevice` function in MATLAB / RunMat

Inspecting the active GPU provider

info = gpuDevice();
disp(info.name);

Expected output (in-process provider):

InProcess

Displaying vendor and backend metadata

info = gpuDevice();
fprintf("Vendor: %s (backend: %s)\n", info.vendor, info.backend);

Expected output:

Vendor: RunMat (backend: inprocess)

Checking whether double precision is supported

info = gpuDevice();
if info.supports_double
    disp("Double precision kernels are available.");
else
    disp("Provider only exposes single precision.");
end

Formatting a user-facing status message

summary = gpuInfo();
disp("Active GPU summary:");
disp(summary);

Expected output:

Active GPU summary:
GPU[device_id=0, index=1, name='InProcess', vendor='RunMat', backend='inprocess', precision='double', supports_double=true]

Handling missing providers gracefully

try
    info = gpuDevice();
catch ex
    warning("GPU unavailable: %s", ex.message);
end

If no provider is registered:

Warning: GPU unavailable: gpuDevice: no acceleration provider registered

FAQ

Do I need to call `gpuDevice` before using other GPU builtins?

No. RunMat initialises the active provider during startup. gpuDevice is purely informational and can be called at any time to inspect the current provider.

Why are some fields missing from the struct?

Providers only fill metadata they can reliably supply. For example, the in-process test provider does not report memory_bytes. Real GPU backends typically populate additional fields.

What happens if there is no GPU provider?

RunMat raises gpuDevice: no acceleration provider registered. You can catch this error and fall back to CPU code, as shown in the examples above.

Does `gpuDevice` support selecting or resetting devices?

RunMat currently exposes a single provider. gpuDevice(1) returns that provider, matching MATLAB's first-device semantics, while any other index raises gpuDevice: GPU device with index N not available. Reset requests (gpuDevice('reset') or gpuDevice([])) are not implemented yet and return gpuDevice: reset is not supported by the active provider.

How can I get a quick string summary instead of a struct?

Use gpuInfo(). It internally calls gpuDevice and formats the struct fields into a concise status string that is convenient for logging or display.

What does the gpuDevice function do in MATLAB / RunMat?

How does the gpuDevice function behave in MATLAB / RunMat?

GPU residency in RunMat (Do I need gpuArray?)

Examples of using the gpuDevice function in MATLAB / RunMat