code: public static DMatrixRMaj checkZerosLT(DMatrixRMaj A , int numRows , int numCols) {
          if( A == null ) {
              return new DMatrixRMaj(numRows,numCols);
          }  else if( numRows != A.numRows || numCols != A.numCols ) {
              A.reshape(numRows,numCols);
              A.zero();
          } else {
              for( int i = 0; i < A.numRows; i++ ) {
                  int index = i*A.numCols;
                  int end = index + Math.min(i,A.numCols);;
                  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.