code: public int[] getNonZeroIndices() {
          int[] nz = new int[negativeDimensions.length 
                             + positiveDimensions.length];
          System.arraycopy(negativeDimensions, 0, nz, 
                           0, negativeDimensions.length);
          System.arraycopy(positiveDimensions, 0, nz, 
                           negativeDimensions.length, positiveDimensions.length);
          return nz;
      }
docs: {@inheritDoc} Note that this method is <i>not</i> constant time; this
  method runs in time proportional the the number of non-zero indices.