Merge pull request #722 from JuliaControl/tfs

allow char when creating tf(s)

Author: baggepinnen

src/types/tf.jl

@@ -72,12 +72,12 @@ function tf(G::TransferFunction{TE,<:SisoTf{T}}) where {TE<:TimeEvolution,T<:Num
 end
 
 # Function for creation of 's' or 'z' var
-function tf(var::AbstractString)
-    var != "s" && error("""var must be 's' for continuous time tf. Call tf("z", Ts) for a discrete-time variable.""")
+function tf(var::Union{AbstractString, Char})
+    var ∉ ("s", 's') && error("""var must be 's' for continuous time tf. Call tf("z", Ts) for a discrete-time variable.""")
     return tf([1, 0], [1], Continuous())
 end
-function tf(var::AbstractString, Ts::Real)
-    var != "z" && error("var must be 'z' for discrete-time tf.")
+function tf(var::Union{AbstractString, Char}, Ts::Real)
+    var ∉ ("z", 'z') && error("var must be 'z' for discrete-time tf.")
     Ts == 0 && error("Ts must not be 0 for discrete-time tf.")
     return tf([1, 0], [1], Discrete(Ts))
 end

test/test_transferfunction.jl

@@ -5,6 +5,7 @@
 # type: C: Continuous, D: Discrete
 # dims: "npnuny" (np = # poles)
 s = tf("s")
+@test s == tf('s')
 @inferred 1.0/s
 @inferred 1/s
 
@@ -16,6 +17,7 @@ C_221 = @inferred tf(vecarray(1, 2,[1, 2, 3], [1, 2]), vecarray(1, 2, [1, 8, 15]
 C_222 = [C_221; C_221]
 C_022 = @inferred tf(4*[1 0; 0 1])
 s = @inferred tf("s")
+s = @inferred tf('s')
 
 # DISCRETE
 D_111 = @inferred tf([1, 2], [1, -0.5], 0.005)