Unable to compile Libtorch with Plumed

Hello, I am trying to use Plumed 2.9.0 with Pytorch/Libtorch (CPU version) in the perspective of using it with CPMD to run enhanced sampling MD using machine-learned collective variables (generated by mlcolvars using Pytorch). If I try to run ./configure, I have different issues depending on the choice of the C++ compiler. I have tried both 2.0.0 and 2.3.0 versions of Pytorch/Libtorch, with or without C++11 ABIs, to no avail. The machine on which I am trying to install this runs under Rocky Linux release 9.2 (Blue Onyx).

I was also trying to install Plumed, Libtorch and Pytorch using conda (which works) but I understand Plumed installed in this way is already compiled and cannot be set up with optional modules? So compiling is the only way to have optional modules?

I have enabled the environment variables as indicated in the installation guide. Here is the ./configure command that I run (based on recommendations in earlier issues):

./configure --prefix=/home/ac276447/mimic_sources/plumed-2.9.0/plumed-install/ --enable-libtorch LDFLAGS="-L/home/ac276447/mimic_sources/other-libtorch/libtorch-2.3.0-cxx11/lib"  CPPFLAGS='-I/home/ac276447/mimic_sources/other-libtorch/libtorch-2.3.0-cxx11/include -I/home/ac276447/mimic_sources/other-libtorch/libtorch-2.3.0-cxx11/include/torch/csrc/api/include/'

Adding the --enable-modules=pytorch option does not change anything.

The following commands have all been run with Libtorch 2.3.0, C++11 ABI, CPU version.

With default (`mpiicpc`) and `mpiicc`:

This is set up as the CXX environment variable, because it is what I found to work with other programs. Setting it explicitly in ./configure does not change anything. The following lines appear when running ./configure but are skipped quickly:

checking whether mpiicpc accepts -std=c++14... yes
checking libtorch without extra libs... no
checking libtorch with  -ltorch_cpu -lc10... no
configure: WARNING: cannot enable __PLUMED_HAS_LIBTORCH

plus a bunch of errors looking like this:

In file included from /usr/local/install/gcc-13.1.0/include/c++/13.1.0/cwchar(44),
                 from /usr/local/install/gcc-13.1.0/include/c++/13.1.0/bits/postypes.h(40),
                 from /usr/local/install/gcc-13.1.0/include/c++/13.1.0/iosfwd(42),
                 from /usr/local/install/gcc-13.1.0/include/c++/13.1.0/ios(40),
                 from /usr/local/install/gcc-13.1.0/include/c++/13.1.0/ostream(40),
                 from /usr/local/install/gcc-13.1.0/include/c++/13.1.0/iostream(41),
                 from conftest.cpp(1):
/usr/include/wchar.h(397): error: identifier "_Float32" is undefined
  extern _Float32 wcstof32 (const wchar_t *__restrict __nptr,

I am guessing that Plumed tries to use gcc at some point (?).

There is also this error when running it with Libtorch 2.3.0:

/home/ac276447/mimic_sources/other-libtorch/libtorch-2.3.0-cxx11/include/torch/csrc/api/include/torch/all.h:4:2: error: #error C++17 or later compatible compiler is required to use PyTorch.

Invoking the compiler with -v gives:

mpiicc for the Intel(R) MPI Library 2021.10 for Linux*
Copyright Intel Corporation.
icc: remark #10441: The Intel(R) C++ Compiler Classic (ICC) is deprecated and will be removed from product release in the second half of 2023. The Intel(R) oneAPI DPC++/C++ Compiler (ICX) is the recommended compiler moving forward. Please transition to use this compiler. Use '-diag-disable=10441' to disable this message.
icc version 2021.10.0 (gcc version 13.1.0 compatibility)

With `gcc`

When trying to set CXX=gcc: the "checking libtorch" lines have the same output but are much longer to pass (around 10s for each), the gcc-related errors disappear and the config.log file is much bigger (32MB compared to 650kB). Of course Plumed says that it will not be configured with MPI.

gcc -v gives:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/install/gcc-13.1.0/libexec/gcc/x86_64-pc-linux-gnu/13.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/usr/local/install/gcc-13.1.0 --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.1.0 (GCC)

With `mpic++`, `mpiCC`, `mpicxx`, `mpigxx`, `mpicc`, `mpigcc`

Same thing as above, except the MPI configuration message.

Invoking them with -v gives (mpic++, mpiCC):

Using built-in specs.
COLLECT_GCC=/usr/local/install/gcc-13.1.0/bin/g++
COLLECT_LTO_WRAPPER=/usr/local/install/gcc-13.1.0/libexec/gcc/x86_64-pc-linux-gnu/13.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/usr/local/install/gcc-13.1.0 --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.1.0 (GCC)

Or this (mpicxx, mpigxx):

mpigxx for the Intel(R) MPI Library 2021.10 for Linux*
Copyright Intel Corporation.
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/local/install/gcc-13.1.0/libexec/gcc/x86_64-pc-linux-gnu/13.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/usr/local/install/gcc-13.1.0 --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.1.0 (GCC)

Or this (mpicc, mpigcc):

mpigcc for the Intel(R) MPI Library 2021.10 for Linux*
Copyright Intel Corporation.
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/local/install/gcc-13.1.0/libexec/gcc/x86_64-pc-linux-gnu/13.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/usr/local/install/gcc-13.1.0 --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.1.0 (GCC)

With `mpiicx` and `mpiicpx`

Same output as above, the "checking libtorch" lines are passed much more quickly but the config.log file is much smaller only 225kB now.

I believe these compilers do not work at all for me as invoking them with -v gives:

Intel(R) oneAPI DPC++/C++ Compiler 2023.2.0 (2023.2.0.20230622)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/bin-llvm
Configuration file: /usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/bin-llvm/../bin/icpx.cfg
Found candidate GCC installation: /usr/local/install/gcc-13.1.0/lib/gcc/x86_64-pc-linux-gnu/13.1.0
Selected GCC installation: /usr/local/install/gcc-13.1.0/lib/gcc/x86_64-pc-linux-gnu/13.1.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
 "/usr/bin/ld" --hash-style=gnu --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out /lib/../lib64/crt1.o /lib/../lib64/crti.o /usr/local/install/gcc-13.1.0/lib/gcc/x86_64-pc-linux-gnu/13.1.0/crtbegin.o -L/usr/local/install/intel/intel-hpc-2023.2.0/mpi/2021.10.0/lib/release -L/usr/local/install/intel/intel-hpc-2023.2.0/mpi/2021.10.0/lib -L/usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/compiler/lib/intel64_lin -L/usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/bin-llvm/../lib -L/usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/compiler/lib/intel64_lin -L/usr/local/install/gcc-13.1.0/lib/gcc/x86_64-pc-linux-gnu/13.1.0 -L/usr/local/install/gcc-13.1.0/lib/gcc/x86_64-pc-linux-gnu/13.1.0/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/local/install/gcc-13.1.0/lib/gcc/x86_64-pc-linux-gnu/13.1.0/../../.. -L/usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/bin-llvm/../lib -L/lib -L/usr/lib -L/usr/local/install/intel/intel-hpc-2023.2.0/tbb/2021.10.0/env/../lib/intel64/gcc4.8 -L/usr/local/install/intel/intel-hpc-2023.2.0/mpi/2021.10.0//libfabric/lib -L/usr/local/install/intel/intel-hpc-2023.2.0/mpi/2021.10.0//lib/release -L/usr/local/install/intel/intel-hpc-2023.2.0/mpi/2021.10.0//lib -L/usr/local/install/intel/intel-hpc-2023.2.0/mkl/2023.2.0/lib/intel64 -L/usr/local/install/intel/intel-hpc-2023.2.0/ippcp/2021.8.0/lib/intel64 -L/usr/local/install/intel/intel-hpc-2023.2.0/ipp/2021.9.0/lib/intel64 -L/usr/local/install/intel/intel-hpc-2023.2.0/dnnl/2023.2.0/cpu_dpcpp_gpu_dpcpp/lib -L/usr/local/install/intel/intel-hpc-2023.2.0/dal/2023.2.0/lib/intel64 -L/usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/compiler/lib/intel64_lin -L/usr/local/install/intel/intel-hpc-2023.2.0/compiler/2023.2.0/linux/lib -L/usr/local/install/intel/intel-hpc-2023.2.0/ccl/2021.10.0/lib/cpu_gpu_dpcpp -L/home/ac276447/mimic_sources/other-libtorch/libtorch-2.0.0-precxx11/lib -L/home/ac276447/.local/lib -L. --enable-new-dtags -rpath /usr/local/install/intel/intel-hpc-2023.2.0/mpi/2021.10.0/lib/release -rpath /usr/local/install/intel/intel-hpc-2023.2.0/mpi/2021.10.0/lib -lmpicxx -lmpifort -lmpi -ldl -lrt -lpthread -Bstatic -lsvml -Bdynamic -Bstatic -lirng -Bdynamic -lstdc++ -Bstatic -limf -Bdynamic -lm -lgcc_s -lgcc -Bstatic -lirc -Bdynamic -ldl -lgcc_s -lgcc -lc -lgcc_s -lgcc -Bstatic -lirc_s -Bdynamic /usr/local/install/gcc-13.1.0/lib/gcc/x86_64-pc-linux-gnu/13.1.0/crtend.o /lib/../lib64/crtn.o
/usr/bin/ld: /lib/../lib64/crt1.o: in function `_start':
(.text+0x1b): undefined reference to `main'
icpx: error: linker command failed with exit code 1 (use -v to see invocation)

Other potentially concerning errors that I systematically see in the ./configure output are these (just before the checking libtorch lines):

checking fftw3.h usability... no
checking fftw3.h presence... no
checking for fftw3.h... no
configure: WARNING: cannot enable __PLUMED_HAS_FFTW
checking for python... python
configure: Python executable is python
checking support for required python modules (python3, setuptools, cython)... no
configure: WARNING: cannot enable python interface

Does anyone have ideas about how to solve this? Is this due to a missing option, a wrong version of the compiler? Please let me know what further tests or details I could do to solve this.

Attached: the config.log files obtained with mpic++, mpiicx, and mpiicc with Libtorch 2.3.0 CPU version. plumed_conf_issues.zip

plumed / plumed2