code: public static ZMatrixRMaj checkZerosLT(ZMatrixRMaj A , int numRows , int numCols) {
          if( A == null ) {
              return new ZMatrixRMaj(numRows,numCols);
          } else if( numRows != A.numRows || numCols != A.numCols )
              throw new IllegalArgumentException("Input is not "+numRows+" x "+numCols+" matrix");
          else {
              for( int i = 0; i < A.numRows; i++ ) {
                  int index = i*A.numCols*2;
                  int end = index + Math.min(i,A.numCols)*2;;
                  while( index < end ) {
                      A.data[index++] = 0;
                  }
              }
          }
          return A;
      }
docs: Creates a zeros matrix only if A does not already exist.  If it does exist it will fill
  the lower triangular portion with zeros.