docs: public static boolean isNegative(ZMatrixD1 a, ZMatrixD1 b, double tol) {
          if( a.numRows != b.numRows || a.numCols != b.numCols )
              throw new IllegalArgumentException("Matrix dimensions must match");
  
          int length = a.getNumElements()*2;
  
          for( int i = 0; i < length; i++ ) {
              if( !(Math.abs(a.data[i]+b.data[i]) <= tol) )
                  return false;
          }
  
          return true;
      }