Add mindegree, maxdegree, extdegree (#77)

* Add mindegree, maxdegree, extdegree

* Use in flat

docs/src/moments.md

@@ -30,6 +30,9 @@ that is, it implements the following two functions
 ```@docs
 MultivariatePolynomials.variables(::MultivariateMoments.Measure)
 MultivariatePolynomials.monomials(::MultivariateMoments.Measure)
+MultivariatePolynomials.maxdegree(::MultivariateMoments.Measure)
+MultivariatePolynomials.mindegree(::MultivariateMoments.Measure)
+MultivariatePolynomials.extdegree(::MultivariateMoments.Measure)
 moments
 ```
 

src/flat.jl

@@ -79,7 +79,7 @@ function compute_support!(
     solver::FlatExtension,
 ) where {T}
     μ = measure(ν)
-    d = MP.maxdegree(μ.x)
+    d = MP.maxdegree(μ)
     v = MP.variables(μ)
     d0 = div(d - 1, 2)
     d1 = d - 1 - d0

src/measure.jl

@@ -65,6 +65,27 @@ Returns an iterator over the monomials of `μ` sorted in the decreasing order.
 """
 MP.monomials(μ::Measure) = μ.x
 
+"""
+    maxdegree(μ::AbstractMeasureLike)
+
+Returns the maximal degree of the monomials of `μ`.
+"""
+MP.maxdegree(μ::Measure) = MP.maxdegree(MP.monomials(μ))
+
+"""
+    mindegree(μ::AbstractMeasureLike)
+
+Returns the minimal degree of the monomials of `μ`.
+"""
+MP.mindegree(μ::Measure) = MP.mindegree(MP.monomials(μ))
+
+"""
+    extdegree(μ::AbstractMeasureLike)
+
+Returns the extremal degrees of the monomials of `μ`.
+"""
+MP.extdegree(μ::Measure) = MP.extdegree(MP.monomials(μ))
+
 """
     moments(μ::AbstractMeasureLike)
 

test/measure.jl

@@ -3,6 +3,9 @@
     @test_throws ArgumentError measure([1, 2], [x, x * y, y])
     @test_throws ArgumentError measure([1, 2, 3, 4], [x, x * y, y])
     μ = measure([1, 0, 2, 3], [x^2 * y^2, y * x^2, x * y * x^2, x * y^2])
+    @test MP.mindegree(μ) == 3
+    @test MP.maxdegree(μ) == 4
+    @test MP.extdegree(μ) == (3, 4)
     @test monomials(μ) ==
           monomial_vector([x^3 * y, x^2 * y^2, x^2 * y, x * y^2])
     @test monomial.(moments(μ)) ==