remove private methods; update readme

README.md

@@ -21,7 +21,7 @@ The core data structure in Plasmo.jl is the `OptiGraph`. The optigraph contains
 
 ## License
 
-Plasmo is licensed under the [MPL 2.0 license](https://github.com/plasmo-dev/Plasmo.jl/blob/main/LICENSE.md).
+Plasmo.jl is licensed under the [MPL 2.0 license](https://github.com/plasmo-dev/Plasmo.jl/blob/main/LICENSE.md).
 
 ## Installation
 
@@ -98,8 +98,23 @@ If you find Plasmo.jl useful for your work, you may cite the [manuscript](https:
   journal={Mathematical Programming Computation},
   year={2022},
   volume={14},
-  pages={699 - 747}
+  pages={699 - 747},
+  doi={10.1007/s12532-022-00223-3}
 }
 ```
-There is also a freely available [pre-print](https://arxiv.org/abs/2006.05378).
-
+You can also access a freely available [pre-print](https://arxiv.org/abs/2006.05378).
+
+There is also an earlier manuscript where we presented the initial ideas behind Plasmo.jl which you can find
+[here](https://www.sciencedirect.com/science/article/abs/pii/S0098135418312687):
+``` sourceCode
+@article{JalvingCaoZavala2019,
+author = {Jalving, Jordan and Cao, Yankai and Zavala, Victor M},
+journal = {Computers {\&} Chemical Engineering},
+pages = {134--154},
+title = {Graph-based modeling and simulation of complex systems},
+volume = {125},
+year = {2019},
+doi = {10.1016/j.compchemeng.2019.03.009}
+}
+```
+A pre-print of this paper can be found [here](https://arxiv.org/abs/1812.04983)

docs/src/index.md

@@ -79,7 +79,7 @@ pages = {134--154},
 title = {Graph-based modeling and simulation of complex systems},
 volume = {125},
 year = {2019},
-doi = {https://doi.org/10.1016/j.compchemeng.2019.03.009}
+doi = {10.1016/j.compchemeng.2019.03.009}
 }
 ```
 A pre-print of this paper can also be found [here](https://arxiv.org/abs/1812.04983)

src/backends/moi_backend.jl

@@ -701,7 +701,11 @@ function _copy_subgraph_edges!(backend::GraphMOIBackend, subgraph::OptiGraph)
     end
 end
 
-# TODO: re-implement MOIU._is_variable_function
+# copied from: https://github.com/jump-dev/MathOptInterface.jl/blob/a15b67fe47ad20caf316eb1bba0369a46ceb5a34/src/Utilities/copy.jl#L268-L270
+_is_variable_function(::Type{MOI.VariableIndex}) = true
+_is_variable_function(::Type{MOI.VectorOfVariables}) = true
+_is_variable_function(::Any) = false
+
 function _copy_node_to_backend!(backend::GraphMOIBackend, node::OptiNode)
     dest = backend
     index_map = MOIU.IndexMap()
@@ -715,13 +719,13 @@ function _copy_node_to_backend!(backend::GraphMOIBackend, node::OptiNode)
     # we try to constrain variables on creation.
     all_constraint_types = MOI.get(node, MOI.ListOfConstraintTypesPresent())
     variable_constraint_types = filter(all_constraint_types) do (F, S)
-        return MOIU._is_variable_function(F)
+        return _is_variable_function(F)
     end
     _copy_element_constraints(dest, node, index_map, variable_constraint_types)
 
     # copy non-variable constraints
     nonvariable_constraint_types = filter(all_constraint_types) do (F, S)
-        return !MOIU._is_variable_function(F)
+        return !_is_variable_function(F)
     end
     _copy_element_constraints(dest, node, index_map, nonvariable_constraint_types)
     return nothing