Better way to handle polar notation

src/SinusoidalRegressions.jl

@@ -9,7 +9,8 @@ export sinfit_j, mixlinsinfit_j,
        ieee1057,
        rmse, mae,
        SinusoidalFunctionParameters,
-       SinusoidP, MixedLinearSinusoidP
+       SinusoidP, MixedLinearSinusoidP,
+       torect
 
 include("typedefs.jl")
 include("jacquelin_sr.jl")
@@ -46,6 +47,14 @@ function mae(fit::T, exact::T, x) where {T <: SinusoidalFunctionParameters}
     return sum(abs.(fitvalues .- exactvalues))/length(x)
 end
 
+"""
+    torect(M, θ)
+
+Convert polar coordinates to rectangular coordinates `(y, x)` where ``x = M\\cos(θ)`` and
+``y = -M\\sin(θ)``
+"""
+torect(M, θ) = (-M*sin(θ), M*cos(θ))
+
 ## Precompilation
 @precompile_setup begin
     x = [-1.983, -1.948, -1.837, -1.827, -1.663, -0.815, -0.778, -0.754, -0.518,  0.322,  0.418,  0.781,

src/typedefs.jl

@@ -25,13 +25,12 @@ struct SinusoidP{T <: Real} <: SinusoidalFunctionParameters
 end
 
 """
-    SinusoidP{T}(f, DC, Q, I ; polar = false)
+    SinusoidP{T}(f, DC, Q, I)
 
 Construct a `SinusoidP{T}` with the given parameters, promoting to a common type `T` if
 necessary.
 
-If the keyword argument `polar` is `true`, then the arguments are interpreted as frequency,
-DC, amplitude `A` and phase `ϕ` in the model ``s(x) = DC + A\\cos(2πfx + ϕ)``.
+To express the model as ``s(x) = M\\cos(2πfx + θ)``, use the `torect` function.
 
 Examples
 ========
@@ -44,23 +43,15 @@ Sinusoidal parameters SinusoidP{Float64}:
   Sine amplitude (Q)  : -0.5
   Cosine amplitude (I): 1.2
 
-julia> SinusoidP(1, 0, 1, 0, polar = true)  # A pure cosine
+julia> SinusoidP(1, 0, torect(1, -π/2)...)  # A pure sine
 Sinusoidal parameters SinusoidP{Float64}:
   Frequency (Hz)      : 1.0
   DC                  : 0.0
-  Sine amplitude (Q)  : -0.0
-  Cosine amplitude (I): 1.0
+  Sine amplitude (Q)  : 1.0
+  Cosine amplitude (I): 0.0
 ```
 """
-function SinusoidP(f, DC, Q, I ; polar = false)
-    if polar
-        # argument Q is amplitude; I is phase
-        cosamp = Q*cos(I)
-        sinamp = -Q*sin(I)
-        return SinusoidP(promote(f, DC, sinamp, cosamp)...)
-    end
-    SinusoidP(promote(f, DC, Q, I)...)
-end
+SinusoidP(f, DC, Q, I) = SinusoidP(promote(f, DC, Q, I)...)
 
 """
     SinusoidP{T}(; f, DC, Q, I)

test/runtests.jl

@@ -35,17 +35,22 @@ using Test
 end
 
 @testset "Polar notation for SinusoidP" begin
-    s = SinusoidP(1, 0, 1, 0, polar = true) # A pure cosine
+    s = SinusoidP(1, 0, torect(1, 0)...) # A pure cosine
     @test s.f == 1
     @test s.DC == 0
     @test s.Q ≈ 0
     @test s.I ≈ 1
-    s = SinusoidP(1, 0, 1, -π/2, polar = true) # A pure sine
+    s = SinusoidP(1, 0, torect(1, -π/2)...) # A pure sine
     @test s.f == 1
     @test s.DC == 0
     @test s.Q ≈ 1 atol = 1e-12
     @test s.I ≈ 0 atol = 1e-12
-    s = SinusoidP(1, 5, 1, -π/4, polar = true) # A mix
+    s = SinusoidP(1, 0, torect(1, 3π/2)...) # Another pure sine
+    @test s.f == 1
+    @test s.DC == 0
+    @test s.Q ≈ 1 atol = 1e-12
+    @test s.I ≈ 0 atol = 1e-12
+    s = SinusoidP(1, 5, torect(1, -π/4)...) # A mix
     @test s.f == 1
     @test s.DC == 5
     @test s.Q ≈ sqrt(2)/2 atol = 1e-12