Add ExponentialTransiogram

src/GeoStatsFunctions.jl

@@ -69,36 +69,37 @@ export
 
   # theoretical variograms
   Variogram,
-  NuggetEffect,
   GaussianVariogram,
+  SphericalVariogram,
   ExponentialVariogram,
   MaternVariogram,
-  SphericalVariogram,
   CubicVariogram,
   PentasphericalVariogram,
-  PowerVariogram,
   SineHoleVariogram,
   CircularVariogram,
+  PowerVariogram,
+  NuggetEffect,
   NestedVariogram,
   sill,
   nugget,
   structures,
 
   # theoretical covariances
   Covariance,
-  CircularCovariance,
-  CubicCovariance,
-  ExponentialCovariance,
   GaussianCovariance,
+  SphericalCovariance,
+  ExponentialCovariance,
   MaternCovariance,
+  CubicCovariance,
   PentasphericalCovariance,
   SineHoleCovariance,
-  SphericalCovariance,
+  CircularCovariance,
 
   # theoretical transiograms
   Transiogram,
   LinearTransiogram,
   SphericalTransiogram,
+  ExponentialTransiogram,
   MatrixExponentialTransiogram,
   PiecewiseLinearTransiogram,
 

src/theoretical/transiogram.jl

@@ -26,5 +26,6 @@ isstationary(::Type{<:Transiogram}) = true
 
 include("transiogram/linear.jl")
 include("transiogram/spherical.jl")
+include("transiogram/exponential.jl")
 include("transiogram/matrixexponential.jl")
 include("transiogram/piecewiselinear.jl")

src/theoretical/transiogram/exponential.jl

@@ -0,0 +1,32 @@
+# ------------------------------------------------------------------
+# Licensed under the MIT License. See LICENSE in the project root.
+# ------------------------------------------------------------------
+
+"""
+    ExponentialTransiogram(; ranges, proportions)
+    ExponentialTransiogram(ball; proportions)
+
+A spherical transiogram with `ranges`, and `proportions`.
+Optionally, use a custom metric `ball`.
+"""
+struct ExponentialTransiogram{P,B} <: Transiogram
+  prop::P
+  ball::B
+end
+
+ExponentialTransiogram(ball; proportions=(0.5, 0.5)) = ExponentialTransiogram(proportions, ball)
+
+ExponentialTransiogram(; ranges=(1.0u"m", 1.0u"m"), proportions=(0.5, 0.5)) =
+  ExponentialTransiogram(proportions, MetricBall(ranges))
+
+constructor(::ExponentialTransiogram) = ExponentialTransiogram
+
+function (t::ExponentialTransiogram)(h)
+  r = radius(t.ball)
+  p = t.prop
+  L = length(p)
+  h′, r′ = unitless(h, r)
+  v = 1 - exp(-3(h′ / r′))
+  T = typeof(p[1] * v)
+  SMatrix{L,L}(i == j ? T(1 - (1 - p[j]) * v) : T((p[j] * v)) for i in 1:L, j in 1:L)
+end

src/theoretical/variogram.jl

@@ -129,13 +129,13 @@ end
 # ----------------
 
 include("variogram/gaussian.jl")
-include("variogram/exponential.jl")
 include("variogram/spherical.jl")
+include("variogram/exponential.jl")
 include("variogram/matern.jl")
 include("variogram/cubic.jl")
 include("variogram/pentaspherical.jl")
 include("variogram/sinehole.jl")
+include("variogram/circular.jl")
 include("variogram/power.jl")
 include("variogram/nugget.jl")
-include("variogram/circular.jl")
 include("variogram/nested.jl")