.. currentmodule:: playdoh

.. _example-gpu:

Example: gpu
============

Example of :func:`map` with a function loading CUDA code and running on GPUs.

::

    from playdoh import *
    from numpy import *
    import pycuda
    
    
    # The function loading the CUDA code
    def fun(scale):
        # The CUDA code, which multiplies a vector by a scale factor.
        code = '''
        __global__ void test(double *x, int n)
        {
         int i = blockIdx.x * blockDim.x + threadIdx.x;
         if(i>=n) return;
         x[i] *= %d;
        }
        ''' % scale
    
        # Compile the CUDA code to GPU code
        mod = pycuda.compiler.SourceModule(code)
    
        # Transform the CUDA function into a Python function
        f = mod.get_function('test')
    
        # Create a vector on the GPU filled with 8 ones
        x = pycuda.gpuarray.to_gpu(ones(8))
    
        # Start the function on the GPU
        f(x, int32(8), block=(8, 1, 1))
    
        # Load the result from the GPU to the CPU
        y = x.get()
    
        # Finally, return the result
        return y
    
    # This line is required on Windows, any call to a Playdoh function
    # must be done after this line on this OS.
    # See http://docs.python.org/library/multiprocessing.html#windows
    if __name__ == '__main__':
        # Execute ``fun(2)`` and ``fun(3)`` on 1 GPU on this machine
        # and return the result.
        if CANUSEGPU:
            print map(fun, [2, 3], gpu=1)