Add estimator interface and global metric estimator implementation

docs/src/lib/internals/estimator.md

@@ -6,6 +6,16 @@ The interface that has to be implemented for an estimator.
 
 ```@autodocs
 Modules = [MetagraphOptimization]
-Pages = ["models/estimator.jl"]
+Pages = ["estimator/interafce.jl"]
 Order = [:type, :constant, :function]
 ```
+
+## Global Metric Estimator
+
+Implementation of a global metric estimator. It uses the graph properties compute effort, data transfer, and compute intensity.
+
+```@autodocs
+Modules = [MetagraphOptimization]
+Pages = ["estimator/global_metric.jl"]
+Order = [:type, :function]
+```

src/MetagraphOptimization.jl

@@ -122,6 +122,7 @@ include("task/print.jl")
 include("task/properties.jl")
 
 include("estimator/interface.jl")
+include("estimator/global_metric.jl")
 
 include("models/interface.jl")
 include("models/print.jl")

src/estimator/global_metric.jl

@@ -0,0 +1,27 @@
+
+"""
+   CDCost
+
+Representation of a [`DAG`](@ref)'s cost as estimated by the [`GlobalMetricEstimator`](@ref).
+
+# Fields:
+`.data`: The total data transfer.\\
+`.computeEffort`: The total compute effort.\\
+`.computeIntensity`: The compute intensity, will always equal `.computeEffort / .data`.
+"""
+const CDCost = NamedTuple{(:data, :computeEffort, :computeIntensity), Tuple{Float64, Float64, Float64}}
+
+struct GlobalMetricEstimator <: AbstractEstimator end
+
+function cost_type(estimator::GlobalMetricEstimator)
+    return CDCost
+end
+
+function graph_cost(estimator::GlobalMetricEstimator, graph::DAG)
+    properties = get_properties(graph)
+    return (
+        data = properties.data,
+        computeEffort = properties.computeEffort,
+        computeIntensity = properties.computeIntensity,
+    )::CDCost
+end

src/estimator/interface.jl

@@ -10,6 +10,13 @@ Interface functions are
 """
 abstract type AbstractEstimator end
 
+"""
+    cost_type(estimator::AbstractEstimator)
+
+Interface function returning a specific estimator's cost type, i.e., the type returned by its implementation of [`graph_cost`](@ref) and [`operation_effect`](@ref).
+"""
+function cost_type end
+
 """
     graph_cost(estimator::AbstractEstimator, graph::DAG)
 
@@ -21,5 +28,16 @@ function graph_cost end
     operation_effect(estimator::AbstractEstimator, graph::DAG, operation::Operation)
 
 Get the estimated effect on the cost of the graph, such that `graph_cost(estimator, graph) + operation_effect(estimator, graph, operation) ~= graph_cost(estimator, graph_with_operation_applied)`. There is no hard requirement for this, but the better the estimate, the better an optimization algorithm will be.
+
+!!! note
+    There is a default implementation of this function, applying the operation, calling [`graph_cost`](@ref), then popping the operation again.
+    
+    It can be much faster to overload this function for a specific estimator and directly compute the effects from the operation if possible.
 """
-function operation_effect end
+function operation_effect(estimator::AbstractEstimator, graph::DAG, operation::Operation)
+    cost = graph_cost(estimator, graph)
+    push_operation!(graph, operation)
+    cost_after = graph_cost(estimator, graph)
+    pop_operation!(graph)
+    return cost_after - cost
+end