Changes

=== Nvidia HPC SDK [https://developer.nvidia.com/hpc-sdk] ===Evolved from PGI Compiler community edition. Installation guide are provided in the official website. Currently only supports Linux systems, but Windows support will come soon.<source>wget https://developer.download.nvidia.com/hpc-sdk/20.9/nvhpc-20-9_20.9_amd64.deb \

https://developer.download.nvidia.com/hpc-sdk/20.9/nvhpc-2020_20.9_amd64.deb sudo apt-get install ./nvhpc-20-9_20.9_amd64.deb ./nvhpc-2020_20.9_amd64.deb</source> After installation, the compilers can be found under <code>/opt/nvidia/hpc_sdk/Linux_x86_64/20.9/compilers/bin</code>, and OpenACC code can be compiled with <code>nvc -acc -gpu=manage demo.c</code>, where <code>-acc</code> indicates that the code will include OpenACC directives, and <code>-gpu=manage</code> indicates how should memory be managed. <code>nvc</code> is used here because source code is C code, there is <code>nvc++</code> for compiling C++ code. The compiler can also tell how the parallel regions are generalized if you pass in a <code>-Minfo</code> option like<source>$ nvc -acc -gpu=managed -Minfo demo.cmain: 79, Generating implicit copyin(A[:256][:256]) [if not already present] Generating implicit copy(_error) [if not already present] Generating implicit copyout(Anew[1:254][1:254]) [if not already present] 83, Loop is parallelizable 85, Loop is parallelizable Accelerator kernel generated Generating Tesla code 83, #pragma acc loop gang, vector(4) /* blockIdx.y threadIdx.y */ Generating implicit reduction(max:_error) 85, #pragma acc loop gang, vector(32) /* blockIdx.x threadIdx.x */ 91, Generating implicit copyout(A[1:254][1:254]) [if not already present] Generating implicit copyin(Anew[1:254][1:254]) [if not already present] 95, Loop is parallelizable 97, Loop is parallelizable Accelerator kernel generated Generating Tesla code 95, #pragma acc loop gang, vector(4) /* blockIdx.y threadIdx.y */ 97, #pragma acc loop gang, vector(32) /* blockIdx.x threadIdx.x */</source>This tells which loops are parallelized with line numbers for reference. For Windows users that would like to try this SDK, WSL2 is one way to go. === GCC [https://gcc.gnu.org/wiki/OpenACC] ===

We are comparing with OpenMP for two reasons. First, OpenMP is also based on directives to parallelize code; second, OpenMP started support of offloading to accelerators starting OpenMP 4.0 using `<code>target` </code> constructs. OpenACC uses directives to tell the compiler where to parallelize loops, and how to manage data between host and accelerator memories. OpenMP takes a more generic approach, it allows programmers to explicitly spread the execution of loops, code regions and tasks across teams of threads.