To access an external model from Eikos, an interface must be defined. The structure of the interface is decided by Eikos, but some work is needed for the user to comply with this interface. For example, if the external model is contained in a piece of programming code, some additional code has to be provided by the user to comply with the way Eikos calls the model.

A external model (or some executable user defined wrapper code) is called by Eikos with the command line:

executablefile %inputfile %outputfile %timefile

where executablefile is an .exe or .bat file with the user provided model code, %inputfile and %timefile are file names provided by Eikos at runtime which must be read by the executablefile. %outputfile is also a file name provided by Eikos to which results must be written by executablefile.

%inputfile, %outputfile and %timefile contains values columnwise with columns separated by a user defined delimeter. The delimiter and whether the files should contain headers can be defined in the Eikos GUI. At each iteration of a probabilistic simulation, Eikos calls executablefile with the three files. After the call, Eikos reads the results for the current iteration from %outputfile.

For time dependent models, The outputfile must contain values of each time point. If the outputs e.g. are O1, O2 and 3 time points defined, the output file should be on a format similar to (only the column delimiter may differ):

O1      O1      O1      O2      O2      O2
v1t1   v1t2   v1t3   v2t1   v2t2   v2t3

where vitk are value of output i at timepoint k.