code: private static File getTempMatrixFile() {
          File tmp = null;
          try {
              tmp = File.createTempFile("matlab-sparse-matrix", ".dat");
          } catch (IOException ioe) {
              throw new IOError(ioe);
          }
          tmp.deleteOnExit();
          return tmp;
      }
docs: Returns a temporary file that will be deleted on JVM exit.
  '
  @return a temporary file used to store a matrix