Change one coefficient in the model. The desired change is captured
Var object, a
Constr object, and a desired
coefficient for the specified variable in the specified constraint.
If you make multiple changes to the same coefficient, the last one
will be applied.
Note that, due to our lazy update approach, the change won't actually take effect until you update the model (using Model.update), optimize the model (using Model.optimize), or write the model to disk (using Model.write).
constr: Constraint for coefficient to be changed.
var: Variable for coefficient to be changed.
newvalue: Desired new value for coefficient.
model.chgCoeff(c0, x, 2.0)