Add doctests

src/Symbolics.jl

@@ -68,7 +68,7 @@ include("complex.jl")
 
 Performs the substitution on `expr` according to rule(s) `s`.
 # Examples
-```julia
+```jldoctest
 julia> @variables t x y z(t)
 4-element Vector{Num}:
     t

src/linear_algebra.jl

@@ -83,7 +83,7 @@ Currently only works if all equations are linear. `check` if the expr is linear
 w.r.t `vars`.
 
 # Examples
-```julia
+```jldoctest
 julia> @variables x y
 2-element Vector{Num}:
  x

src/taylor.jl

@@ -10,7 +10,7 @@ Return the power series in `x` around `x0` to the powers `ns` with coefficients
 Examples
 ========
 
-```julia
+```jldoctest
 julia> @variables x y[0:3] z
 3-element Vector{Any}:
  x
@@ -47,7 +47,7 @@ Calculate the `n`-th order coefficient(s) in the Taylor series of `f` around `x
 
 Examples
 ========
-```julia
+```jldoctest
 julia> @variables x y
 2-element Vector{Num}:
  x
@@ -101,7 +101,7 @@ If `rationalize`, float coefficients are approximated as rational numbers (this
 
 Examples
 ========
-```julia
+```jldoctest
 julia> @variables x
 1-element Vector{Num}:
  x

src/utils.jl

@@ -27,7 +27,7 @@ Return a vector of variables appearing in `e`, optionally restricting to variabl
 Note that the returned variables are not wrapped in the `Num` type.
 
 # Examples
-```julia
+```jldoctest
 julia> @variables t x y z(t);
 
 julia> Symbolics.get_variables(x + y + sin(z); sort = true)
@@ -97,7 +97,7 @@ Convert a differential variable to a `Term`. Note that it only takes a `Term`
 not a `Num`.
 Any upstream metadata can be passed via `x_metadata`
 
-```julia
+```jldoctest
 julia> @variables x t u(x, t) z(t)[1:2]; Dt = Differential(t); Dx = Differential(x);
 
 julia> Symbolics.diff2term(Symbolics.value(Dx(Dt(u))))
@@ -156,7 +156,7 @@ it will only output `y` instead of `y(t)`.
 
 # Examples
 
-```julia
+```jldoctest
 julia> @variables t z(t)
 2-element Vector{Num}:
     t
@@ -251,7 +251,7 @@ Extract the degree of `p` with respect to `sym`.
 
 # Examples
 
-```julia
+```jldoctest
 julia> @variables x;
 
 julia> Symbolics.degree(x^0)
@@ -305,7 +305,7 @@ Note that `p` might need to be expanded and/or simplified with `expand` and/or `
 
 # Examples
 
-```julia
+```jldoctest
 julia> @variables a x y;
 
 julia> Symbolics.coeff(2a, x)

src/variable.jl

@@ -418,7 +418,7 @@ expr = β[1]* x + y^α + σ(3) * (z - t) - β[2] * w(t - 1)
 
 Symbolics supports creating variables that denote an array of some size.
 
-```julia
+```jldoctest
 julia> @variables x[1:3]
 1-element Vector{Symbolics.Arr{Num, 1}}:
  x[1:3]
@@ -436,7 +436,7 @@ julia> @variables t z(t)[1:3] # also works for dependent variables
 A symbol or expression that represents an array can be turned into an array of
 symbols or expressions using the `scalarize` function.
 
-```julia
+```jldoctest
 julia> Symbolics.scalarize(z)
 3-element Vector{Num}:
  (z(t))[1]
@@ -451,7 +451,7 @@ operator, and in this case, `@variables` doesn't automatically assign the value,
 instead, it only returns a vector of symbolic variables. All the rest of the
 syntax also applies here.
 
-```julia
+```jldoctest
 julia> a, b, c = :runtime_symbol_value, :value_b, :value_c
 (:runtime_symbol_value, :value_b, :value_c)
 
@@ -676,7 +676,7 @@ notation. Use `@variables` instead to create symbolic array variables (as
 opposed to array of variables). See `variable` to create one variable with
 subscripts.
 
-```julia-repl
+```jldoctest
 julia> Symbolics.variables(:x, 1:3, 3:6)
 3×4 Matrix{Num}:
  x₁ˏ₃  x₁ˏ₄  x₁ˏ₅  x₁ˏ₆
@@ -694,7 +694,7 @@ end
 Create a variable with the given name along with subscripted indices with the
 `symtype=T`. When `T=FnType`, it creates a symbolic function.
 
-```julia-repl
+```jldoctest
 julia> Symbolics.variable(:x, 4, 2, 0)
 x₄ˏ₂ˏ₀