From 6ebf0222e7340664f7c833f00ffecccc40f7fe16 Mon Sep 17 00:00:00 2001
From: Emily Bourne <emily.bourne@epfl.ch>
Date: Tue, 21 Apr 2026 09:50:00 +0200
Subject: [PATCH 1/2] Add a dedicated action to install METIS/MUMPS caching the
 result

---
 .github/actions/build/action.yml              | 26 +---------
 .../actions/install-dependencies/action.yml   | 49 +++++++++++++++++++
 2 files changed, 51 insertions(+), 24 deletions(-)
 create mode 100644 .github/actions/install-dependencies/action.yml

diff --git a/.github/actions/build/action.yml b/.github/actions/build/action.yml
index 32018589..db209bb4 100644
--- a/.github/actions/build/action.yml
+++ b/.github/actions/build/action.yml
@@ -14,33 +14,11 @@ runs:
       run: |
         apt-get -qq update
         apt-get -qq -y install lcov
-    - name: Install METIS
-      shell: bash
+    - name: Install MUMPS dependencies
       if: inputs.use-mumps == 'true'
-      run: |
-        apt-get -qq -y install gfortran
-        git clone -b v5.1.0.4 https://github.com/scivision/METIS.git
-        cd METIS
-        cmake -Bbuild -DCMAKE_INSTALL_PREFIX=$(pwd)/install -DCMAKE_BUILD_TYPE=Release
-        cmake --build build
-        cmake --install build
-        ls install/*
-        echo "METIS_DIR=$(pwd)/install" >> $GITHUB_ENV
-        echo "METIS_ROOT=$(pwd)/install" >> $GITHUB_ENV
-    - name: Install MUMPS
-      shell: bash
-      if: inputs.use-mumps == 'true'
-      run: |
-        git clone -b v5.5.1.11 https://github.com/scivision/mumps.git
-        cd mumps
-        cmake -Bbuild -DBUILD_SINGLE=on -DBUILD_DOUBLE=on -Dmetis=on -Dopenmp=on -Dparallel=off -DCMAKE_INSTALL_PREFIX=$(pwd)/install -DCMAKE_BUILD_TYPE=Release -S .
-        cmake --build build
-        cmake --install build
-        ls install/*
-        echo "MUMPS_DIR=$(pwd)/install" >> $GITHUB_ENV
+      uses: ./.github/actions/install-dependencies
     - name: Build
       shell: bash
-      # ensure that the installed compiler version is used
       run: |
         mkdir build && cd build
         export CMAKE_PREFIX_PATH=/opt/openmp
diff --git a/.github/actions/install-dependencies/action.yml b/.github/actions/install-dependencies/action.yml
new file mode 100644
index 00000000..2baa7435
--- /dev/null
+++ b/.github/actions/install-dependencies/action.yml
@@ -0,0 +1,49 @@
+name: "Install Dependencies"
+description: "Install METIS and MUMPS with caching"
+
+runs:
+  using: "composite"
+  steps:
+    - name: Install gfortran
+      shell: bash
+      run: |
+        apt-get -qq -y install gfortran
+    - name: Cache METIS
+      id: cache-metis
+      uses: actions/cache@v4
+      with:
+        path: METIS/install
+        key: metis-v5.1.0.4-${{ runner.os }}
+    - name: Install METIS
+      shell: bash
+      if: steps.cache-metis.outputs.cache-hit != 'true'
+      run: |
+        git clone -b v5.1.0.4 https://github.com/scivision/METIS.git
+        cd METIS
+        cmake -Bbuild -DCMAKE_INSTALL_PREFIX=$(pwd)/install -DCMAKE_BUILD_TYPE=Release
+        cmake --build build
+        cmake --install build
+    - name: Set METIS environment variables
+      shell: bash
+      run: |
+        echo "METIS_DIR=$GITHUB_WORKSPACE/METIS/install" >> $GITHUB_ENV
+        echo "METIS_ROOT=$GITHUB_WORKSPACE/METIS/install" >> $GITHUB_ENV
+    - name: Cache MUMPS
+      id: cache-mumps
+      uses: actions/cache@v4
+      with:
+        path: mumps/install
+        key: mumps-v5.5.1.11-metis-${{ runner.os }}
+    - name: Install MUMPS
+      shell: bash
+      if: steps.cache-mumps.outputs.cache-hit != 'true'
+      run: |
+        git clone -b v5.5.1.11 https://github.com/scivision/mumps.git
+        cd mumps
+        cmake -Bbuild -DBUILD_SINGLE=on -DBUILD_DOUBLE=on -Dmetis=on -Dopenmp=on -Dparallel=off -DCMAKE_INSTALL_PREFIX=$(pwd)/install -DCMAKE_BUILD_TYPE=Release -S .
+        cmake --build build
+        cmake --install build
+    - name: Set MUMPS environment variables
+      shell: bash
+      run: |
+        echo "MUMPS_DIR=$GITHUB_WORKSPACE/mumps/install" >> $GITHUB_ENV

From 852f1c3e415a6124ba6aa0789fcf340d5d5c54dc Mon Sep 17 00:00:00 2001
From: Emily Bourne <emily.bourne@epfl.ch>
Date: Tue, 21 Apr 2026 11:19:32 +0200
Subject: [PATCH 2/2] More explicit

---
 .github/actions/build/action.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/actions/build/action.yml b/.github/actions/build/action.yml
index db209bb4..c9ea7ab2 100644
--- a/.github/actions/build/action.yml
+++ b/.github/actions/build/action.yml
@@ -14,7 +14,7 @@ runs:
       run: |
         apt-get -qq update
         apt-get -qq -y install lcov
-    - name: Install MUMPS dependencies
+    - name: Install additional dependencies to use MUMPS
       if: inputs.use-mumps == 'true'
       uses: ./.github/actions/install-dependencies
     - name: Build