The GEM software project

The Gaussian Emulation Machine (GEM) software project aims to provide user-friendly tools to implement statistical analyses of uncertainty in the outputs of computer models, using the techniques of Gaussian process emulation. To download an introduction to these tools and the concepts that underlie them, click here.

The GEM software available here has been developed by Marc Kennedy for the Centre for Terrestrial Carbon Dynamics (CTCD). CTCD is funded by the Natural Environment Research Council (NERC).

The Gaussian Emulation Machine for Sensitivity Analysis (GEM-SA) is the first product of the GEM project. It will allow you to build an emulator of a computer code from a set of input and output points. It will also perform prediction, uncertainty analysis and sensitivity analysis of the code using far fewer code runs than Monte-Carlo based methods.

GEM-SA is offered free of charge, provided it is not used for profit. It may be freely copied and distributed, provided that files have not been edited or altered in any way, and provided that no charge is made for distributing GEM-SA. Published work that uses GEM-SA results should include a citation for this web page. Requests to use GEM-SA for any commercial purpose must be directed to Marc Kennedy: .

If you do use GEM-SA please let Marc Kennedy know ( and he will add you to the list of users. He will keep registered users informed of bug fixes and updated information about GEM-SA and future developments of the GEM project.

GEM-SA runs on Windows, but Linux users can also run it. The required package (called "Wine") can be freely downloaded in both binary and source form for various Linux distributions from

One Day Course: Uncertainty in Environmental Process Modelling
A course was held on March 21st and March 22nd 2005 for NERC related researchers, which included instruction in the use of GEM-SA. The practical sessions (PowerPoint) are now available for download:

Download instructions
Download V1.1 zip file (1.3MB) MS Windows version.

Extract/unzip the zip file to produce a directory GEM-SA containing the following:

  • GEM-SA.exe, the executable
  • baccodoc.chm, the help file
  • GEM-SA.exe.manifest, used within Windows XP to give the appropriate style windows
  • emulator.doc, a MS-Word document describing how to use the emulator independently of GEM-SA
  • modeldescription.pdf, some brief details of the statistical model used to build the emulator
  • GEM-SA DEMO DATA, a directory containing a number of example code input and output files

The wxWindows toolkit was used for creating the GUI

The second product of the GEM project will be GEM-Cal, which will implement the calibration theory of Kennedy and O'Hagan. A beta test version of GEM-Cal may be downloaded here. Installation is similar to the procedure above for GEM-SA. Please contact Marc Kennedy for further information.

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