A Second Order Differential Equation can be used in a Function Expression or User Subroutines.

The DIF20, DIF21 and DIF22 functions are used to get the state variables in a Function Expression. For more information, see the System Element Functions for function expressions.

The SYSFNC function is used to get the state variables in a User Subroutine. For more information, see the Intrinsic Functions in a User Subroutine for user subroutines.