Built-in variables
threadIdx: thread index within Block
blockIdx: block index within Grid
blockDim: thread shape
GridDim: grid shape
global array id = blockIdx.x * blockDim.x + threadIdx.x
threadIdx: thread index within Block
blockIdx: block index within Grid
blockDim: thread shape
GridDim: grid shape
global array id = blockIdx.x * blockDim.x + threadIdx.x