All machines

Working fortran-95 and C compilers are needed in order to compile Quantum-ESPRESSO. Most so-called ``fortran-90'' compilers implement the fortran-95 standard, but older versions may not be fortran-95 compliant.

If you get ``Compiler Internal Error'' or similar messages, try to lower the optimization level, or to remove optimization, just for the routine that has problems. If it doesn't work, or if you experience weird problems, try to install patches for your version of the compiler (most vendors release at least a few patches for free), or to upgrade to a more recent version.

If you get an error in the loading phase that looks like ``ld: file XYZ.o: unknown (unrecognized, invalid, wrong, missing, ...) file type'', or ``While processing relocatable file XYZ.o, no relocatable objects were found'' (T3E), one of the following things have happened:

1. you have leftover object files from a compilation with another compiler: run make clean and recompile.
2. make does not stop at the first compilation error (it happens with some compilers). Remove file XYZ.o and look for the compilation error.

If many symbols are missing in the loading phase, you did not specify the location of all needed libraries (LAPACK, BLAS, FFTW, machine-specific optimized libraries). If you did, but symbols are still missing, see below (for Linux PC).