= Convergence Problems =
Most interesting engineering problems are highly nonlinear.
This kind of problems are very difficult to solve using Newton's like solvers without a good approximation of the solution.
[wiki:EMSO] assembles the initial guess for a problem from the '''Default''' attribute of the variables.
For several cases this approximation is enough, but for more difficult to converge it is not.
== Initial Guess From Saved Results ==
In some cases the user can obtain a solution for a specific configuration or simplified model.
Examples are:
* To choose simplified thermodynamic models (ideal gas and ideal liquid)
* To supply a specifications or parameter settings which have better convergence characteristics
With a solution at hand, even for unrelated cases, it is much easier for a Newton's like method to obtain the ''final'' solution.
This can be achieved using the '''guessFile''' option:
1. Obtain a solution using simplified models or at conditions with better convergence characteristics
1. Once you got convergence, using the [wiki:EMSO] graphical interface save the result to a file (eg. '''result.rlt''')
1. Use the option '''guessFile="result.rlt"''' on the difficult to converge case, as follows:
{{{
#!mso
FlowSheet MyFlowSheet
...
OPTIONS
guessFile = "result";
end
}}}
Note: This option can be used in both, '''dynamic and static''' simulation.
== Initial Condition From Saved Results ==
Dynamic simulations requires the specification of a initial condition.
In several dynamic simulation experiments the user wants to start the simulation from a previous simulated or steady state point.
In several cases it is very hard to give a steady-state initial condition manually.
For these cases the '''initalFile''' option can be used.
This option is analogous to the '''guessFile''' option but it instructs the simulator to ignore the manually specified initial conditions and to use a previously saved result instead:
{{{
#!mso
FlowSheet MyFlowSheet
...
OPTIONS
initialFile = "result";
end
}}}
Note: This option makes sense '''only for dynamic''' simulations.