Changes the behavior of lazy updates
 Type: int
 Default value: 1
 Minimum value: 0
 Maximum value: 1

Determines how newly added variables and linear constraints are handled. The default setting (1) allows you to use new variables and constraints immediately for building or modifying the model. A setting of 0 requires you to call update before these can be used.

Since the vast majority of programs never query Gurobi for details about the optimization models they build, the default setting typically removes the need to call update, or even be aware of the details of our lazy update approach for handling model modifications. However, these details will show through when you try to query modified model information.

In the Gurobi interface, model modifications (bound changes, right-hand side changes, objective changes, etc.) are placed in a queue. These queued modifications are applied to the model at three times: when you call update, when you call optimize, or when you call write to write the model to disk. When you query information about the model, the result will depend on both whether that information was modified and when it was modified. In particular, if the modification is sitting in the queue, you'll get the result from before the modification. Note that this lazy update behavior is independent of the value of the UpdateMode parameter.

The only potential benefit to changing the parameter to 0 is that in unusual cases this setting may allow simplex make more aggressive use of warm-start information after a model modification.

If you want to change this parameter, you need to set it as soon as you create your Gurobi environment.

Note that you still need to call update to modify an attribute on an SOS constraint, quadratic constraint, or general constraint.

For examples of how to query or modify parameter values from our different APIs, refer to our Parameter Examples.