See if this makes the MPC test more reliable on MacOS

.github/workflows/build_cmake.yml

@@ -29,7 +29,13 @@ jobs:
 
     - name: Build just tests
       working-directory: ${{ github.workspace }}/dlib/test
-      run: cmake --build ${{ env.build_dir }} --config ${{ env.config }} --target dtest --parallel 4
+      run: |
+        if [ "$RUNNER_OS" == "macOS" ]; then
+          # MacOS machines often come with low quality BLAS libraries installed, so don't use those.
+          cmake --build ${{ env.build_dir }} --config ${{ env.config }} --target dtest --parallel 4 -DDLIB_USE_BLAS=0 -DDLIB_USE_LAPACK=0
+        else
+          cmake --build ${{ env.build_dir }} --config ${{ env.config }} --target dtest --parallel 4
+        fi;
 
     - name: Test
       working-directory: ${{ github.workspace }}/dlib/test/${{ env.build_dir }}

dlib/test/mpc.cpp

@@ -403,7 +403,7 @@ namespace
                 dlog << LINFO << trans(alpha2);
                 dlog << LINFO << "objective value:  " << 0.5*trans(alpha)*Q*alpha + trans(b)*alpha;
                 dlog << LINFO << "objective value2: " << 0.5*trans(alpha2)*Q*alpha + trans(b)*alpha2;
-                DLIB_TEST_MSG(max(abs(alpha-alpha2)) < 1e-6, max(abs(alpha-alpha2)));
+                DLIB_TEST_MSG(max(abs(alpha-alpha2)) < 1e-7, max(abs(alpha-alpha2)));
             }
 
             test_with_positive_target_error_thresh();