In Sage I did this:

In Julia I tried doing the ‘same thing’:

```
Plots.GRBackend()
julia> r=25.1; i=0.2;
julia> f(a) = ( 1/2*(pi*a*i/r + 2*r)*cos(a), 1/2*(pi*a*i/r + 2*r)*sin(a) );
julia> plot( f, 0, 248*pi )`
And got this:`ERROR: MethodError: no method matching Float64(::Tuple{Float64, Float64})
Closest candidates are:
(::Type{T})(::AbstractChar) where T<:Union{AbstractChar, Number} at char.jl:50
(::Type{T})(::Base.TwicePrecision) where T<:Number at twiceprecision.jl:243
(::Type{T})(::Complex) where T<:Real at complex.jl:37
...
Stacktrace:
[1] (::RecipesPipeline.var"#7#8"{Symbol})(x::Tuple{Float64, Float64})
@ RecipesPipeline ~\.julia\packages\RecipesPipeline\CirY4\src\utils.jl:201
[2] (::ComposedFunction{RecipesPipeline.var"#7#8"{Symbol}, typeof(f)})(x::Float64) (repeats 2 times)
@ Base .\operators.jl:938
[3] (::PlotUtils.var"#27#29"{ComposedFunction{ComposedFunction{RecipesPipeline.var"#7#8"{Symbol}, typeof(f)}, RecipesPipeline.var"#9#10"{Symbol}}})(x::Float64)
@ PlotUtils ~\.julia\packages\PlotUtils\es5pb\src\adapted_grid.jl:46
[4] _broadcast_getindex_evalf
@ .\broadcast.jl:648 [inlined]
[5] _broadcast_getindex
@ .\broadcast.jl:621 [inlined]
[6] getindex
@ .\broadcast.jl:575 [inlined]
[7] macro expansion
@ .\broadcast.jl:984 [inlined]
[8] macro expansion
@ .\simdloop.jl:77 [inlined]
[9] copyto!
@ .\broadcast.jl:983 [inlined]
[10] copyto!
@ .\broadcast.jl:936 [inlined]
[11] copy
@ .\broadcast.jl:908 [inlined]
[12] materialize
@ .\broadcast.jl:883 [inlined]
[13] adapted_grid(f::ComposedFunction{ComposedFunction{RecipesPipeline.var"#7#8"{Symbol}, typeof(f)}, RecipesPipeline.var"#9#10"{Symbol}}, minmax::Tuple{Float64, Float64}; max_recursions::Int64, max_curvature::Float64)
@ PlotUtils ~\.julia\packages\PlotUtils\es5pb\src\adapted_grid.jl:57
[14] adapted_grid(f::Function, minmax::Tuple{Float64, Float64})
@ PlotUtils ~\.julia\packages\PlotUtils\es5pb\src\adapted_grid.jl:16
[15] _scaled_adapted_grid(f::Function, xscale::Symbol, yscale::Symbol, xmin::Int64, xmax::Float64)
@ RecipesPipeline ~\.julia\packages\RecipesPipeline\CirY4\src\user_recipe.jl:353
[16] macro expansion
@ ~\.julia\packages\RecipesPipeline\CirY4\src\user_recipe.jl:293 [inlined]
[17] apply_recipe(plotattributes::AbstractDict{Symbol, Any}, f::Function, xmin::Number, xmax::Number)
@ RecipesPipeline ~\.julia\packages\RecipesBase\92zOw\src\RecipesBase.jl:282
[18] _process_userrecipes!(plt::Any, plotattributes::Any, args::Any)
@ RecipesPipeline ~\.julia\packages\RecipesPipeline\CirY4\src\user_recipe.jl:36
[19] recipe_pipeline!(plt::Any, plotattributes::Any, args::Any)
@ RecipesPipeline ~\.julia\packages\RecipesPipeline\CirY4\src\RecipesPipeline.jl:70
[20] _plot!(plt::Plots.Plot, plotattributes::Any, args::Any)
@ Plots ~\.julia\packages\Plots\lzHOt\src\plot.jl:172
[21] plot(::Any, ::Vararg{Any, N} where N; kw::Any)
@ Plots ~\.julia\packages\Plots\lzHOt\src\plot.jl:58
[22] plot(::Any, ::Any, ::Vararg{Any, N} where N)
@ Plots ~\.julia\packages\Plots\lzHOt\src\plot.jl:52
[23] top-level scope
@ REPL[4]:1
```