[section:gpu Support for GPU programming in Boost.Math]

[h4 GPU Support]

Selected functions, distributions, tools, etc. support running on both host and devices.
These functions will have the annotation `BOOST_MATH_GPU_ENABLED` or `BOOST_MATH_CUDA_ENABLED` next to their individual documentation.
Functions marked with `BOOST_MATH_GPU_ENABLED` are tested using CUDA (both NVCC and NVRTC) as well as SYCL to provide a wide range of support.
Functions marked with `BOOST_MATH_CUDA_ENABLED` are few, but due to its restrictions SYCL is unsupported.

[h4 Policies]

The default policy on all devices is ignore error due to the lack of throwing ability.
A user can specify their own policy like usual, but when the code is run on device it will be ignored.

[h4 How to build with device support]

When compiling with CUDA or SYCL you will have to ensure that your code is being run inside of a kernel function.
It is not enough to simply compile existing code with the NVCC compiler to run the code on the device.
A simple CUDA kernel to run the Beta Distribution CDF on NVCC would be:

    __global__ void cuda_beta_dist(const double* in, double* out, int num_elements)
    {
        const int i = blockDim.x * blockIdx.x + threadIdx.x;

        if (i < num_elements)
        {
            out[i] = cdf(boost::math::beta_distribution<double>(), in[i]);
        }
    }

And on CUDA on NVRTC:

    const char* cuda_kernel = R"(
    #include <boost/math/distributions/beta.hpp>
    extern "C" __global__ 
    void test_beta_dist_kernel(const double* in, double* out, int num_elements)
    {
        const int i = blockDim.x * blockIdx.x + threadIdx.x;
        if (i < num_elements)
        {
            out[i] = boost::math::cdf(boost::math::beta_distribution<double>(), in[i]);
        }
    }
    )";

And lastly on SYCL:

    void sycl_beta_dist(const double* in, double* out, int num_elements, sycl::queue& q)
    {
        q.submit([&](sycl::handler& h) {
            h.parallel_for(sycl::range<1>(num_elements), [=](sycl::id<1> i) {
                out[i] = boost::math::cdf(boost::math::beta_distribution<double>(), in[i]);
            });
        });
    }

When using SYCL you must define BOOST_MATH_ENABLE_SYCL, since device support is opt-in on that platform.
For NVCC and NVRTC device support is enabled automatically.

Once your kernel function has been written then use the framework mechanism for launching the kernel.

[endsect] [/section:gpu Support for GPU programming in Boost.Math]

[/ 
  Copyright 2024. Matt Borland
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]

