Print an error if non-positive dt is detected (#192)

Print an error if non-positive `dt` is detected when constructing an integrator. A negative timesteps can be attained with a mutable update, e.g. `dyn.Δt *= -1`.

Also deprecate `Base.copy(::Langevin)`. We might add it back depending on the resolution to #193. The story here will continue to evolve, but for now it's safe to err on the side of a thinner public API.

src/Integrators.jl

@@ -19,11 +19,12 @@ mutable struct Langevin
     Δt  :: Float64
     λ   :: Float64
     kT  :: Float64
-end
-
-Langevin(Δt; λ, kT) = Langevin(Δt, λ, kT)
 
-Base.copy(dyn::Langevin) = Langevin(dyn.Δt, dyn.λ, dyn.kT)
+    function Langevin(Δt; λ, kT)
+        Δt <= 0 && error("Select positive Δt")
+        return new(Δt, λ, kT)
+    end    
+end
 
 """
     ImplicitMidpoint(Δt::Float64; atol=1e-12) where N
@@ -39,10 +40,12 @@ periods of simulation time.
 mutable struct ImplicitMidpoint
     Δt   :: Float64
     atol :: Float64
-end
-
-ImplicitMidpoint(Δt; atol=1e-12) = ImplicitMidpoint(Δt, atol)
 
+    function ImplicitMidpoint(Δt; atol=1e-12)
+        Δt <= 0 && error("Select positive Δt")
+        return new(Δt, atol)
+    end    
+end
 
 
 ################################################################################
@@ -210,4 +213,4 @@ function rhs_ll!(ΔZ, HZ, integrator, sys)
     for site in eachsite(sys)
         ΔZ[site] = - Δt*im*HZ[site]
     end
-end
+end

src/deprecated.jl

@@ -17,3 +17,8 @@ end
 
 Base.@deprecate suggest_magnetic_supercell(qs, latsize) suggest_magnetic_supercell(qs)
 Base.@deprecate offline_viewers() ()
+
+function Base.copy(dyn::Langevin)
+    @warn "Base.copy(dyn::Langevin) will soon be removed! Use `Langevin(dyn.Δt; dyn.λ, dyn.kT)` instead."
+    Langevin(dyn.Δt; dyn.λ, dyn.kT)
+end

test/test_jet.jl

@@ -16,7 +16,7 @@
         sampler = LocalSampler(kT=0.2; propose)
         @test_opt step!(sys, sampler)
 
-        langevin = Langevin(0.01, kT=0.2, λ=0.1)
+        langevin = Langevin(0.01; kT=0.2, λ=0.1)
         @test_opt step!(sys, langevin)
 
         integrator = ImplicitMidpoint(0.01)
@@ -48,7 +48,7 @@ end
         step!(sys, sampler)
         @test 0 == @allocated step!(sys, sampler)
 
-        langevin = Langevin(0.01, kT=0.2, λ=0.1)
+        langevin = Langevin(0.01; kT=0.2, λ=0.1)
         step!(sys, langevin)
         @test 0 == @allocated step!(sys, langevin)
 

test/test_samplers.jl

@@ -72,7 +72,7 @@
         collect_dur = 100.0
 
         sys = su3_anisotropy_model(; D, L, seed=0)
-        langevin = Langevin(Δt; kT=0.0, λ)
+        langevin = Langevin(Δt; kT=0, λ)
 
         for kT in kTs
             langevin.kT = kT
@@ -96,7 +96,7 @@
         collect_dur = 200.0
 
         sys = su5_anisotropy_model(; D, L, seed=0)
-        langevin = Langevin(Δt; kT=0.0, λ)
+        langevin = Langevin(Δt; kT=0, λ)
 
         for kT ∈ kTs
             langevin.kT = kT