model test
! Simple process model with PI controller

parameter
! These are quantities which are known, but which
! the user may wish to change to see their effect
 mu=1 ;  s = 0.5 ; ti = 10
 t1=1 ; t2 = 1.3 
! They will normally be given initial values
end parameter

variable
! These are the variables or unknowns of the problem
 u, e, ei=0
 x, y 
end variable

Equation
! These are the equations
 e = s-y
 u  =  mu*(e + ei/ti) ! This is the controller algebraic equation
 .ei = e  ! integral action

! These are differential equations representing the process...
 .x = (u-x) / T1
 .y = (x-y) / T2

end equation

initial
 x = 1
 y = 0
end initial

schedule
! This section defines how the model will be run
 deltat=0.2 ! Timestep
 steps=50   ! number of timesteps
end 

end model