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  <title>Matrix transpose in-place</title>
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<body>
  <h1>Square in-place transpose</h1>
  <p>Edit <code>a</code>, then <strong>Run</strong>. Swaps above the diagonal only.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function transposeInPlace(a) {
        var n = a.length;
        var i, j, temp;
        for (i = 0; i < n; i++) {
          for (j = i + 1; j < n; j++) {
            temp = a[i][j];
            a[i][j] = a[j][i];
            a[j][i] = temp;
          }
        }
      }
      function pushMatrix(lines, title, m) {
        lines.push(title);
        var i, j, line, n = m.length;
        for (i = 0; i < n; i++) {
          line = "";
          for (j = 0; j < n; j++) {
            line += m[i][j] + " ";
          }
          lines.push(line);
        }
      }
      var a = [
        [1, 2, 3],
        [4, 5, 6],
        [7, 8, 9]
      ];
      var lines = [];
      pushMatrix(lines, "Before:", a);
      transposeInPlace(a);
      lines.push("");
      pushMatrix(lines, "After (in-place A^T):", a);
      document.getElementById("out").textContent = lines.join("\n");
    })();
  </script>
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JavaScript Matrix Transpose — In-place 3×3 (Try It)