One can run the same component models simultaneously or sequentially by defining the appropriate LAG and SEQ indices. In the example illustrated on figure 4.9, the models perform their prism_put_proto and prism_get_proto calls exactly as in the first lag example above (see 1. of 4.8.1): model A receives and then sends ; its timestep length is 4. During a coupling timestep, model B receives and then sends ; its timestep length is 6. and coupling periods are both 12. By defining a LAG index of -8 for , the models will now run sequentially.
As the LAG for is positive (6), a reading of in its coupling restart file is automatically performed by OASIS3 to fulfill the initial prism_get_proto. As the LAG for is negative (-8), no reading from file is performed initially and model B waits; at time 8, a sending action is effectively performed below model A prism_put_proto (as 8 + LAG (-8) = 0 which is the first coupling timestep) and matches the initial model B prism_get_proto. Below the last model A prism_put_proto of the run at time 116, a sending action is effectively performed, as is a coupling period (as the LAG is negative, the field is not written to its coupling restart file). Below the last model B prism_put_proto of the run at time 114, a writing of to its restart file is performed, as is a coupling period and as the LAG is positive.
If the coupling fields are transformed through OASIS3 executable, it is important to indicate a sequence index. In fact, at each OASIS3 coupling timestep, must be necessarily treated after . Therefore, and .