Added a module DemoSystems.

Author: olof3

src/ControlSystems.jl

@@ -78,7 +78,7 @@ export  LTISystem,
         pade,
         # demo systems
         ssrand,
-        systemdepot,
+        DemoSystems, # A module containing some example systems
         # utilities
         num,    #Deprecated
         den,    #Deprecated

src/demo_systems.jl

@@ -26,59 +26,69 @@ ssrand(T::Type, n; kwargs...) = ssrand(T, n, n, 2*n; kwargs...)
 
 
 """
-    systemdepot(sysname::String; Ts=nothing, kwargs...)
+    DemoSystems
 
-Convenience function for setting up some different systems
-that are commonly used as examples in the control literature.
+A module containing some different systems that are commonly used as examples in the control literature.
 
-Change the default parameter values by using keyword arguments.
+Change the default parameter values using keyword arguments.
 
 SISO systems
 ============
-1) `fo`     First-order system  `1/(sT+1)`
-2) `fotd`   First-order system with time-delay `exp(-sτ)/(sT+1)`
-3) `sotd`   Second-order non-resonant system with time-delay `exp(-sτ)/(sT+1)/(sT2 + 1)`
-4) `resonant`   Second-order resonant systems `ω0^2/(s^2 + 2ζ*ω0*s + ω0^2)`
+* `DemoSystems.fo(;T=1)`     First-order system  `1/(sT+1)`
+* `DemoSystems.fotd(;T=1, τ=1)`   First-order system with time delay `exp(-sτ)/(sT+1)`
+* `DemoSystems.sotd(;T=1, T2=10, τ=1)`   Second-order non-resonant system with time delay `exp(-sτ)/(sT+1)/(sT2 + 1)`
+* `DemoSystems.resonant(;ω0=1, ζ=0.25)`   Second-order resonant systems `ω0^2/(s^2 + 2ζ*ω0*s + ω0^2)`
 
 MIMO systems
 ============
-5) `woodberry`   Wood--Berry distillation column
-6) `doylesat`    Doyle's spinning body example
-"""
-function systemdepot(sysname::String; Ts=nothing, kwargs...)
-    if sysname == "woodberry" # The Wood--Berry distillation column
-        sys = woodberry(;kwargs...)
-    elseif sysname == "fotd"
-        sys = fotd(;kwargs...)
-    elseif sysname == "sotd"
-        sys = sotd(;kwargs...)
-    elseif sysname == "fo"
-        sys = first_order_system(;kwargs...)
-    elseif sysname == "resonant"
-        sys = resonant(;kwargs...)
-    elseif sysname == "doylesat"
-        sys = doylesat(;kwargs...)
-    else
-        error("Unknown system name: $sysname")
-    end
+* `DemoSystems.woodberry()`     Wood--Berry distillation column
+* `DemoSystems.doylesat(;a=10)`    The spinning body example by Doyle
 
-    if isnothing(Ts)
-        return sys
-    else
-        Tsc2d(sys, Ts)
-    end
-end
+Fore more information, see the help for the specific systems.
+"""
+module DemoSystems
+
+using ControlSystems
+using LinearAlgebra
+
+
+"""
+    fo(;T=1, τ=1)
 
-first_order_system(;T=1) = ss(-1/T, 1, 1/T, 0)
+Returns a first-order system `1/(sT+1)` (`StateSpace`).
+"""
+fo(;T=1) = ss(-1/T, 1, 1/T, 0)
+
+
+"""
+    fotd(;T=1, τ=1)
+
+Returns a first-order system + a time delay `exp(-sτ)/(sT+1)` (`DelayLTISystem`).
+"""
 fotd(;T=1, τ=1) = ss(-1/T, 1, 1/T, 0) * delay(τ)
+
+
+"""
+    sotd(;T=1, T2=10, τ=1)
+
+Returns a second-order system + a time delay `exp(-sτ)/(sT+1)/(sT2 + 1)` (`DelayLTISystem`).
+"""
 sotd(;T=1, T2=10, τ=1) = ss(-1/T, 1, 1/T, 0)*ss(-1/T2, 1, 1/T2, 0)*delay(τ)
+
+
+"""
+    resonant(;ω0=1, ζ=0.25)
+
+Returns a second-order system + a time delay `exp(-sτ)/(sT+1)/(sT2 + 1)` (`DelayLTISystem`).
+"""
 resonant(;ω0=1, ζ=0.25) = ss([-ζ -ω0; ω0 -ζ], [ω0; 0], [0 ω0], 0) # QUESTION: Is this the form that we like? Perhhaps not.
 
 
 """
-Doyle's spinning body (satellite) example
-======================
-A classic example that illustrates that robustness analysis of MIMO systems
+    `doylesat(;a=10) = ss([0 a; -a 0], I(2), [1 a; -a 1], 0)`
+
+Returns a model for the spinning body (satellite) example by Doyle,
+which is a classic example that illustrates that robustness analysis of MIMO systems
 is more involved than for SISO systems.
 
 *References:*
@@ -93,9 +103,9 @@ doylesat(;a=10) = ss([0 a; -a 0], I(2), [1 a; -a 1], 0)
 
 
 """
-Wood--Berry distillation column
-======================
-A classic example from the literature on process control of MIMO process.
+    `woodberry()`
+
+Returns a model for the Wood--Berry distillation column, which is a classic example from the literature on process control of MIMO process.
 
 *References:*
 
@@ -108,3 +118,6 @@ function woodberry()
     return [12.8/(1 + 16.7*s)*delay(1.0)   -18.9/(1 + 21*s) * delay(3.0)
             6.6/(1 + 10.9*s) * delay(7.0)  -19.4/(1 + 14.4*s) * delay(3.0)]
 end
+
+
+end