Issue 320 (#321)

* change printing to work with Symbolics; close #320

* version bump [ci skip]

Project.toml

@@ -2,7 +2,7 @@ name = "Polynomials"
 uuid = "f27b6e38-b328-58d1-80ce-0feddd5e7a45"
 license = "MIT"
 author = "JuliaMath"
-version = "2.0.1"
+version = "2.0.2"
 
 [deps]
 Intervals = "d8418881-c3e1-53bb-8760-2df7ec849ed5"

docs/src/extending.md

@@ -25,6 +25,7 @@ As always, if the default implementation does not work or there are more efficie
 | `domain` | x | Should return an  [`AbstractInterval`](https://invenia.github.io/Intervals.jl/stable/#Intervals-1) |
 | `vander` | | Required for [`fit`](@ref) |
 | `companion` | | Required for [`roots`](@ref) |
+| `fromroots` | | By default, will form polynomials using `prod(variable(::P) - r)` for reach root `r`|
 | `*(::P, ::P)` | | Multiplication of polynomials |
 | `divrem` | | Required for [`gcd`](@ref)|
 | `one`| | Convenience to find constant in new basis |

src/polynomials/standard-basis.jl

@@ -2,11 +2,11 @@ abstract type StandardBasisPolynomial{T,X} <: AbstractPolynomial{T,X} end
 
 function showterm(io::IO, ::Type{<:StandardBasisPolynomial}, pj::T, var, j, first::Bool, mimetype) where {T}
 
-    if iszero(pj) return false end
+    if pj === zero(T) return false end
 
     pj = printsign(io, pj, first, mimetype)
 
-    if !(pj == one(T) && !(showone(T) || j == 0))
+    if !(pj === one(T) && !(showone(T) || j == 0))
         printcoefficient(io, pj, j, mimetype)
     end
 

src/show.jl

@@ -13,7 +13,7 @@ hasneg(::Type{T}) where {T} = false
 isneg(pj::T) where {T} = hasneg(T) && pj < zero(T)
 
 "Make `pj` positive if it is negative. (Don't call `abs` as that may not be defined, or appropriate.)"
-aspos(pj::T) where {T} = (hasneg(T) && isneg(pj)) ? -pj : pj
+aspos(pj::T) where {T} = (hasneg(T) && isneg(pj)===true) ? -pj : pj
 
 "Should a value of `one(T)` be shown as a coefficient of monomial `x^i`, `i >= 1`? (`1.0x^2` is shown, `1 x^2` is not)"
 showone(::Type{T}) where {T} = true
@@ -163,7 +163,7 @@ function showterm(io::IO, ::Type{AbstractPolynomial}, pj::T, var, j, first::Bool
 ## print the sign
 ## returns aspos(pj)
 function printsign(io::IO, pj::T, first, mimetype) where {T}
-    neg = isneg(pj)
+    neg = hasneg(T) && isneg(pj) === true
     if first
         neg && print(io, showop(mimetype, "l-"))    #Prepend - if first and negative
     else