Merge pull request #520 from NREL-SIIP/cb/handle-origin-costs

pwl-origin-cost

src/models/operational_cost.jl

@@ -43,7 +43,7 @@ end
 """
     get_slopes(vc::VariableCost{Vector{NTuple{2, Float64}}})
 
-Calculates the slopes for the variable cost represented as a piece wise linear cost function. This function returns n - slopes for n - piecewise linear elements in the function. The first element of the return array corresponds to the average cost at the minimum operating point. If your formulation uses n -1 slopes, you can disregard the first component of the array.
+Calculates the slopes for the variable cost represented as a piece wise linear cost function. This function returns n - slopes for n - piecewise linear elements in the function. The first element of the return array corresponds to the average cost at the minimum operating point. If your formulation uses n -1 slopes, you can disregard the first component of the array. If the first point in the variable cost has a quantity of 0.0, the first slope returned will be 0.0, otherwise, the first slope represents the trajectory to get from the origin to the first point in the variable cost.
 
 """
 function get_slopes(vc::VariableCost{Vector{NTuple{2, Float64}}})
@@ -55,7 +55,7 @@ function get_slopes(vc::Vector{NTuple{2, Float64}})
     previous = (0.0, 0.0)
     for (ix, component) in enumerate(vc)
         if ix == 1
-            slopes[ix] = component[1] / component[2]
+            slopes[ix] = component[2] == 0.0 ? 0.0 : component[1] / component[2] # if the cost component starts at the y-origin make the first slope 0.0
             previous = component
             continue
         end