Explicit Runge-Kutta methods are characterized by a strictly lower triangular ma-trix A, i.e., aij = 0 if j ≥ i. Moreover, the coefficients ci and aij are connected by the condition. i = 1, 2, . . . , ν. This says that ci is the row sum of the i-th row of the matrix A. This condition is required to have a method of order one, i.e., for consistency.