Merge pull request #42 from tpapp/tp/notes-about-derivatives

add a note about derivatives

.github/workflows/CI.yml

@@ -19,7 +19,6 @@ jobs:
         version:
           - '1.6' # Replace this with the minimum Julia version that your package supports. E.g. if your package requires Julia 1.5 or higher, change this to '1.5'.
           - '1' # Leave this line unchanged. '1' will automatically expand to the latest stable 1.x release of Julia.
-          - 'nightly'
         os:
           - ubuntu-latest
         arch:

Project.toml

@@ -1,7 +1,7 @@
 name = "SpectralKit"
 uuid = "5c252ae7-b5b6-46ab-a016-b0e3d78320b7"
 authors = ["Tamas K. Papp <[email protected]>"]
-version = "0.11.1"
+version = "0.11.2"
 
 [deps]
 ArgCheck = "dce04be8-c92d-5529-be00-80e4d2c0e197"

src/derivatives.jl

@@ -83,6 +83,18 @@ zeros from left to right, starting after the highest explicitly assigned tag.
 Consequently, for most applications, you only need to specify tags if you want a different
 nesting than left-to-right.
 
+# Important note about transformations
+
+Always use `derivatives` *before* a transformation for correct results. For example, for some
+transformation `I` and value `x` in the transformed domain,
+```julia
+basis_at(basis2, to_pm1(I, derivatives(x))) # right
+```
+instead of
+```julia
+basis_at(basis2, derivatives(to_pm1(I, x))) # WRONG
+```
+
 # Univariate example
 
 ```jldoctest

src/generic_api.jl

@@ -164,7 +164,7 @@ for this when it makes sense.
 The collocation matrix may not be an `AbstractMatrix`, all it needs to support is `C \\ y`
 for compatible vectors `y = f.(x)`.
 
-Methods are type stable.
+Methods are type stable. The elements of `x` can be [`derivatives`](@ref).
 """
 function collocation_matrix(basis, x = grid(basis))
     @argcheck isconcretetype(eltype(x))