title: How to change default GCC compiler to be used with MPI on Linux CentOS
body: <p>I have two GCC compilers installed on a Linux (CentOS) machine. The old version of GCC (4.4.7) is in the default folder (came with CentOS) and the newer one that I intend to use is in /usr/local/gcc/4.9.3/. My code utilizes MPI and LAPACK/LAPACKE/BLAS libraries and with the old GCC I used to compile source (for example “main.cpp”) like this:</p>
  
  <p><strong>mpiCC main.cpp -o main -L/home/USER1/lapack-3.6.1 -llapacke -llapack -lblas -lm –Wall</strong></p>
  
  <p>This still invokes the old GCC 4.4.7. What should I modify so the above MPI compilation (mpiCC) invokes GCC 4.9.3 executable from the new location at /usr/local/gcc/4.9.3/el6/bin/ ?</p>
  
  <p>From MPICH Installer's Guide version 3.2 (page 6):</p>
  
  <p>"The MPICH configure step will attempt to find the C, C++, and Fortran compilers for you, but if you either want to override the default or need to specify a compiler that configure doesn't recognize, you can specify them on the command line [...]. For example, to select the Intel compilers instead of the GNU compilers on a system with both, use" </p>
  
  <p><code>./configure CC=icc CXX=icpc F77=ifort FC=ifort ...</code></p>
  
  <p>Is there a way to dicriminate between different version of GCC compilers in <code>./configure</code> ? </p>