code: public static MatrixAccumulator asSumAccumulator(final double neutral) {
          return new MatrixAccumulator() {
              private BigDecimal result = BigDecimal.valueOf(neutral);
  
              @Override
              public void update(int i, int j, double value) {
                  result = result.add(BigDecimal.valueOf(value));
              }
  
              @Override
              public double accumulate() {
                  double value = result.setScale(Matrices.ROUND_FACTOR, RoundingMode.CEILING).doubleValue();
                  result = BigDecimal.valueOf(neutral);
                  return value;
              }
          };
      }
docs: Creates a sum matrix accumulator that calculates the sum of all elements in the matrix.
  
  @param neutral the neutral value
  
  @return a sum accumulator