fixed docstring for freqresp, closes JuliaControl#461

src/freqresp.jl

@@ -1,24 +1,24 @@
-"""sys_fr = freqresp(sys, w)
+""" freqresp(G, Ω) -> G_fr
 
-Evaluate the frequency response of a linear system
-
-`w -> C*((iw*im -A)^-1)*B + D`
-
-of system `sys` over the frequency vector `w`."""
-@autovec () function freqresp(sys::LTISystem, w_vec::AbstractVector{<:Real})
+Evaluate the frequency response of the linear system `G` at frequencies `Ω`.
+(for a discrete-system with sample time `Ts` the frequency repsonse is evaluated in
+points `exp.(Ω*(im*Ts))` on the unit circle.
+"""
+@autovec () function freqresp(G::LTISystem, Ω::AbstractVector{<:Real})
     # Create imaginary freq vector s
-    if iscontinuous(sys)
-        s_vec = im*w_vec
+    if iscontinuous(G)
+        s_vec = im*Ω
     else
-        s_vec = exp.(w_vec*(im*sys.Ts))
+        s_vec = exp.(Ω*(im*G.Ts))
     end
-    #if isa(sys, StateSpace)
-    #    sys = _preprocess_for_freqresp(sys)
+    #if isa(G, StateSpace)
+    #    G = _preprocess_for_freqresp(G)
     #end
-    ny,nu = noutputs(sys), ninputs(sys)
-    [evalfr(sys[i,j], s)[] for s in s_vec, i in 1:ny, j in 1:nu]
+    ny, nu = size(G)
+    [evalfr(G[i,j], s)[] for s in s_vec, i in 1:ny, j in 1:nu]
 end
 
+
 # Implements algorithm found in:
 # Laub, A.J., "Efficient Multivariable Frequency Response Computations",
 # IEEE Transactions on Automatic Control, AC-26 (1981), pp. 407-408.