Install MPI on your MAC, where GCC is already installed.
install the following blog instructions to install MPI.
https://blog.csdn.net/yaochuyi/article/details/86939352
S1 double-click the downloaded file openmpi-4.0.0.tar.gz
S2 open CMD, CD to the unzipped folder.
S3 type CD/Users/ycy/Desktop/openmpi – 4.0.0
S4 installed under/usr/local, execute./configure.
S5 enter./configure –prefix=/usr/local
But it turns out that something went wrong, and it went as follows:

*** Startup tests
checking build system type... x86_64-apple-darwin18.5.0
checking host system type... x86_64-apple-darwin18.5.0
checking target system type... x86_64-apple-darwin18.5.0
checking for gcc... x86_64-apple-darwin13.4.0-clang
checking whether the C compiler works... no
configure: error: in `/Users/xxx/openmpi-4.0.2':
configure: error: C compiler cannot create executables
See `config.log' for more details

What’s wrong with the C compiler?But my GCC is clearly installed correctly.
check, may be a permission problem. Then change the S5 command to
sudo./configure –prefix=/usr/local
. Installation successful.