order of derivative to which occurs in , or if does not occur in . For the pendulum DAE above, the variables are . The corresponding signature matrix is See also Algebraic differential equation, a different concept despite the similar name Delay differential equation Partial differential algebraic equation Modelica Language References Further reading Books (Covers the structural approach to computing the DAE index.) Various papers External links http://www.scholarpedia.org/article/Differential-algebraic_equations Differential equations Numerical analysis Differential calculus