title: What are matrixes in GitHub Actions?
body: <p>GitHub released their alternative CI system called Actions. Various workflows from the marketplace, such as <a href="https://github.com/actions/setup-node" rel="nofollow noreferrer">setup-node</a>, have "Matrix testing" examples in their README:</p>
  
  <pre><code>jobs:
    build:
      runs-on: ubuntu-16.04
      strategy:
        matrix:
          node: [ '10', '8' ]
      name: Node ${{ matrix.node }} sample
      steps:
        - uses: actions/checkout@v1
        - name: Setup node
          uses: actions/setup-node@v1
          with:
            node-version: ${{ matrix.node }}
        - run: npm install
        - run: npm test
  </code></pre>
  
  <p>I used CircleCI before but never stumbled upon this concept. Is it some kind of parallel computation?</p>