wait

GPU operations in MATLAB® run asynchronously, that is they run in the background and are not necessarily complete when a subsequent line of code is run. This is relevant when timing code running on a GPU.

You can time how long a function takes to execute on the GPU using the gputimeit function, which ensures that all operations on the GPU have finished before recording the time. As gputimeit runs the function several times, it can be unsuitable for timing particularly long-running code. As an alternative, use the tic and toc functions, calling wait before each.

Select your default GPU device.

gpu = gpuDevice;
disp(gpu.Name + " GPU selected.")

NVIDIA RTX A5000 GPU selected.

Create a 1000-by-1000 matrix containing random numbers on the GPU.

A = rand(1000,"gpuArray");

Wait for the GPU device to finish creating matrix A and start timing using tic.

wait(gpu)
tic

Factorize the matrix into an upper triangular matrix and a permuted lower triangular matrix using the lu function.

[L,U] = lu(A);

Wait for the calculations to finish, then output the elapsed time using toc.

wait(gpu)
toc

Elapsed time is 0.014811 seconds.