🐛 Fix drift implementation

src/models/sarima.jl

@@ -359,9 +359,9 @@ function fit!(model::SARIMAModel;silent::Bool=true,optimizer::DataType=Ipopt.Opt
     fix.(ϵ[1:lb-1],0.0)
 
     if model.seasonality > 1
-        @expression(mod, ŷ[t=lb:T], c + trend*t + sum(β[i]*exogValues[t,i] for i=1:nExog) + sum(ϕ[i]*yValues[t - i] for i=1:model.p) + sum(θ[j]*ϵ[t - j] for j=1:model.q if (t-j > 0)) + sum(Φ[k]*yValues[t - (model.seasonality*k)] for k=1:model.P) + sum(Θ[w]*ϵ[t - (model.seasonality*w)] for w=1:model.Q if (t - (model.seasonality*w) > 0)))
+        @expression(mod, ŷ[t=lb:T], c + trend + sum(β[i]*exogValues[t,i] for i=1:nExog) + sum(ϕ[i]*yValues[t - i] for i=1:model.p) + sum(θ[j]*ϵ[t - j] for j=1:model.q if (t-j > 0)) + sum(Φ[k]*yValues[t - (model.seasonality*k)] for k=1:model.P) + sum(Θ[w]*ϵ[t - (model.seasonality*w)] for w=1:model.Q if (t - (model.seasonality*w) > 0)))
     else
-        @expression(mod, ŷ[t=lb:T], c + trend*t + sum(β[i]*exogValues[t,i] for i=1:nExog) + sum(ϕ[i]*yValues[t - i] for i=1:model.p) + sum(θ[j]*ϵ[t - j] for j=1:model.q if (t-j > 0)))
+        @expression(mod, ŷ[t=lb:T], c + trend + sum(β[i]*exogValues[t,i] for i=1:nExog) + sum(ϕ[i]*yValues[t - i] for i=1:model.p) + sum(θ[j]*ϵ[t - j] for j=1:model.q if (t-j > 0)))
     end
 
     includeModelConstraints!(mod, yValues, T, lb, objectiveFunction)
@@ -1002,7 +1002,7 @@ function auto(
     end
 
     allowMean = isnothing(allowMean) ? (d+D == 0) : allowMean  
-    allowDrift = isnothing(allowDrift) ?  (d+D >= 1) : allowDrift
+    allowDrift = isnothing(allowDrift) ?  (d+D == 1) : allowDrift
 
     # Include initial models
     candidateModels = Vector{SARIMAModel}()