Update README

README.md

@@ -54,7 +54,7 @@ for (i,t) = enumerate(0:h:duration)
     @periodically h begin
         y[i] = measure(P)
         r[i] = reference(t)
-        u[i] = control(i)
+        u[i] = calc_control(i,y,r)
         control(P, u[i])
     end
 end
@@ -64,13 +64,17 @@ Often one finds the need to implement a stateful controller, i.e., a function
 that has a memory or state. To this end, the function [`sysfilter`](@ref) is
 provided. This function is used to implement control loops where a signal is
 filtered through a dynamical system, i.e., `U(z) = C(z)E(z)`.
-Usage is demonstrated below
+Usage is demonstrated below, which is a simplified implementation of the block
+diagram above (transfer function- and signal names corresponds to the figure).
 ```julia
-stateC = init_sysfilter(C)
+stateG1 = init_sysfilter(G1)
+stateG4 = init_sysfilter(G4)
 function control(i)
-    e = r[i]-y[i]
-    u = sysfilter!(stateC, C, e)
+    rf = sysfilter!(stateG4, G4, r)
+    e  = rf-y
+    u  = sysfilter!(stateG1, G1, e)
 end
 ```
-`C` must here be represented by a [`StateSpace`](http://juliacontrol.github.io/ControlSystems.jl/latest/lib/constructors/#ControlSystems.ss) type from [`ControlSystems.jl`](https://github.com/JuliaControl/ControlSystems.jl).
+`G1` and `G4` must here be represented by [`StateSpace`](http://juliacontrol.github.io/ControlSystems.jl/latest/lib/constructors/#ControlSystems.ss) types from [`ControlSystems.jl`](https://github.com/JuliaControl/ControlSystems.jl).
 `TransferFunction` types can easily be converted to a `StateSpace` by `Gss = ss(Gtf)`.
+Continuous time systems can be discretized using `Gd = c2d(Gc, h)`. (The sample time of a process is available through `h = sampletime(P)`.)