get the variable value from list
Answered
I am using call back to solve an LP , when the where value is simplex I am saving the values of a variable in a list called "variables" and send it to a function as follows:
if where == GRB.Callback.SIMPLEX:
# Simplex callback
obj = model.cbGet(GRB.Callback.SPX_OBJVAL)
variables = model.getVars()
getSubSolution(variables)
then I am trying to read the value of the variables as follows:
def getSubSolution(variables):
y = variables
for i in range(1, n):
print(y[i].X)
but I got the following error message :
in gurobipy.__getattr
AttributeError: Unable to retrieve attribute 'X'
moreover, the variables are not ordered in the list :
[<gurobi.Var y10>, <gurobi.Var y15>, <gurobi.Var y19>, <gurobi.Var y35>, <gurobi.Var y1>, <gurobi.Var y2>, <gurobi.Var y3>, <gurobi.Var y4>, <gurobi.Var y5>, <gurobi.Var y6>, <gurobi.Var y7>, <gurobi.Var y8>, <gurobi.Var y9>, <gurobi.Var y11>, <gurobi.Var y12>, <gurobi.Var y13>, <gurobi.Var y14>, <gurobi.Var y16>, <gurobi.Var y17>, <gurobi.Var y18>, <gurobi.Var y20>, <gurobi.Var y21>, <gurobi.Var y22>, <gurobi.Var y23>, <gurobi.Var y24>, <gurobi.Var y25>, <gurobi.Var y26>, <gurobi.Var y27>, <gurobi.Var y28>, <gurobi.Var y29>, <gurobi.Var y30>, <gurobi.Var y31>, <gurobi.Var y32>, <gurobi.Var y33>, <gurobi.Var y34>]
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Gurobi Staff
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There unfortunately isn't a way to query intermediate solution values from the simplex algorithm while it is running. See the Callback Codes section of the documentation for a full list of what can be queried when \( \texttt{where == GRB.Callback.SIMPLEX} \).
Note that the X variable attribute only assumes a value once the optimization is complete. It can't be queried while the optimization is in progress.
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