Added commands to github workflow to ensure that metatensor is instal…

…led so that we can run tests with this code

.github/workflows/linuxWF.yml

@@ -97,6 +97,24 @@ jobs:
         echo "CPATH=$PWD/libtorch/include/torch/csrc/api/include/:$PWD/libtorch/include/:$PWD/libtorch/include/torch:$CPATH" >> $GITHUB_ENV
         echo "INCLUDE=$PWD/libtorch/include/torch/csrc/api/include/:$PWD/libtorch/include/:$PWD/libtorch/include/torch:$INCLUDE" >> $GITHUB_ENV
         echo "PLUMED_CONFIG=$PLUMED_CONFIG --enable-libtorch" >> $GITHUB_ENV
+    - name: Install metatensor
+      if: ${{ ! contains( matrix.variant, '-debug-' ) }} # metatensor is not compiled with GLIBCXX_DEBUG
+      run: |
+        pip install "metatensor-torch ==0.4.0"
+        pip install metatensor-operations metatensor-learn
+        echo "TORCH_CMAKE_PREFIX=$(python -c \"import torch; print(torch.utils.cmake_prefix_path)\")" >> $GITHUB_ENV
+        echo "TORCH_PREFIX=$(cd \"$TORCH_CMAKE_PREFIX/../..\" && pwd)" >> $GITHUB_ENV
+        echo "METATENSOR_CMAKE_PREFIX=$(python -c \"import metatensor; print(metatensor.utils.cmake_prefix_path)\")" >> $GITHUB_ENV
+        echo "METATENSOR_PREFIX=$(cd \"$METATENSOR_CMAKE_PREFIX/../..\" && pwd)" >> $GITHUB_ENV 
+        echo "METATENSOR_TORCH_CMAKE_PREFIX=$(python -c \"import metatensor.torch; print(metatensor.torch.utils.cmake_prefix_path)\")" >> $GITHUB_ENV
+        echo "METATENSOR_TORCH_PREFIX=$(cd \"$METATENSOR_TORCH_CMAKE_PREFIX/../..\" && pwd)" >> $GITHUB_ENV
+        echo "TORCH_CPPFLAGS=\"-D_GLIBCXX_USE_CXX11_ABI=0\""  >> $GITHUB_ENV
+        echo "TORCH_INCLUDES=\"-I$TORCH_PREFIX/include -I$TORCH_PREFIX/include/torch/csrc/api/include\"" >> $GITHUB_ENV
+        echo "CPPFLAGS=\"$TORCH_INCLUDES $TORCH_CPPFLAGS -I$METATENSOR_PREFIX/include -I$METATENSOR_TORCH_PREFIX/include $CPPFLAGS\"" >> $GITHUB_ENV 
+        echo "LDFLAGS=\"-L$TORCH_PREFIX/lib -L$METATENSOR_PREFIX/lib -L$METATENSOR_TORCH_PREFIX/lib $LDFLAGS\"" >> $GITHUB_ENV
+        echo "LDFLAGS=\"$LDFLAGS -Wl,-rpath,$TORCH_PREFIX/lib\"" >> $GITHUB_ENV
+        echo "LDFLAGS=\"$LDFLAGS -Wl,-rpath,$METATENSOR_PREFIX/lib -Wl,-rpath,$METATENSOR_TORCH_PREFIX/lib\"" >> $GITHUB_ENV
+        echo "PLUMED_CONFIG=$PLUMED_CONFIG --enable-libtorch --enable-metatensor" >> $GITHUB_ENV
     - name: Install Doxygen
       if: contains( matrix.variant, '-doc-' )
       run: |