Section: Research Program
Software tools of the team
In addition to the abovementioned research activities, Factas develops and maintains a number of longterm software tools that either implement and illustrate effectiveness of the algorithms theoretically developed by the team or serve as tools to help further research by team members. We present briefly the most important of them.
Pisa
Keywords: Electrical circuit  Stability
Functional Description: To minimise prototyping costs, the design of analog circuits is performed using computeraided design tools which simulate the circuit's response as accurately as possible.
Some commonly used simulation tools do not impose stability, which can result in costly errors when the prototype turns out to be unstable. A thorough stability analysis is therefore a very important step in circuit design. This is where pisa is used.
pisa is a Matlab toolbox that allows designers of analog electronic circuits to determine the stability of their circuits in the simulator. It analyses the impedance presented by a circuit to determine the circuit's stability. When an instability is detected, pisa can estimate location of the unstable poles to help designers fix their stability issue.
Release Functional Description: First version

Authors: Adam Cooman, David Martinez Martinez, Fabien Seyfert and Martine Olivi

Publications: ModelFree ClosedLoop Stability Analysis: A Linear Functional Approach  On Transfer Functions Realizable with Active Electronic Components
DEDALEHF
Scientific Description
DedaleHF consists in two parts: a database of coupling topologies as well as a dedicated predictorcorrector code. Roughly speaking each reference file of the database contains, for a given coupling topology, the complete solution to the coupling matrix synthesis problem (C.M. problem for short) associated to particular filtering characteristics. The latter is then used as a starting point for a predictorcorrector integration method that computes the solution to the C.M. corresponding to the userspecified filter characteristics. The reference files are computed offline using Gröbner basis techniques or numerical techniques based on the exploration of a monodromy group. The use of such continuation techniques, combined with an efficient implementation of the integrator, drastically reduces the computational time.
DedaleHF has been licensed to, and is currently used by TASEspana
Functional Description
DedaleHF is a software dedicated to solve exhaustively the coupling matrix synthesis problem in reasonable time for the filtering community. Given a coupling topology, the coupling matrix synthesis problem consists in finding all possible electromagnetic coupling values between resonators that yield a realization of given filter characteristics. Solving the latter is crucial during the design step of a filter in order to derive its physical dimensions, as well as during the tuning process where coupling values need to be extracted from frequency measurements.
FindSources3D
Keywords: Health  Neuroimaging  Visualization  Compilers  Medical  Image  Processing
FindSources3D is a software program dedicated to the resolution of inverse source problems in electroencephalography (EEG). From pointwise measurements of the electrical potential taken by electrodes on the scalp, FindSources3D estimates pointwise dipolar current sources within the brain in a spherical model.
After a first data transmission “cortical mapping” step, it makes use of best rational approximation on 2D planar crosssections and of the software RARL2 in order to locate singularities. From those planar singularities, the 3D sources are estimated in a last step, see [9].
The present version of FindSources3D (called FindSources3Dbolis) provides a modular, ergonomic, accessible and interactive platform, with a convenient graphical interface for EEG medical imaging. Modularity is now granted (using the tools dtk, Qt, with compiled Matlab libraries). It offers a detailed and nice visualization of data and tuning parameters, processing steps, and of the computed results (using VTK).
A new version is being developed that will incorporate a first Singular Value Decomposition (SVD) step in order to be able to handle time dependent data and to find the corresponding principal static components.

Participants: Juliette Leblond, Maureen Clerc (team Athena, Inria Sophia), JeanPaul Marmorat, Théodore Papadopoulo (team Athena).

URL: http://wwwsop.inria.fr/apics/FindSources3D/en/index.html
PRESTOHF
Scientific Description
For the matrixvalued rational approximation step, PrestoHF relies on RARL2. Constrained realizations are computed using the DedaleHF software. As a toolbox, PrestoHF has a modular structure, which allows one for example to include some building blocks in an already existing software.
The delay compensation algorithm is based on the following assumption: far off the passband, one can reasonably expect a good approximation of the rational components of S11 and S22 by the first few terms of their Taylor expansion at infinity, a small degree polynomial in 1/s. Using this idea, a sequence of quadratic convex optimization problems are solved, in order to obtain appropriate compensations. In order to check the previous assumption, one has to measure the filter on a larger band, typically three times the pass band.
This toolbox has been licensed to (and is currently used by) Thales Alenia Space in Toulouse and Madrid, Thales airborne systems and Flextronics (two licenses). Xlim (University of Limoges) is a heavy user of PrestoHF among the academic filtering community and some free license agreements have been granted to the microwave department of the University of Erlangen (Germany) and the Royal Military College (Kingston, Canada).
Functional Description
PrestoHF is a toolbox dedicated to lowpass parameter identification for microwave filters. In order to allow the industrial transfer of our methods, a Matlabbased toolbox has been developed, dedicated to the problem of identification of lowpass microwave filter parameters. It allows one to run the following algorithmic steps, either individually or in a single stroke:
• Determination of delay components caused by the access devices (automatic reference plane adjustment),
• Automatic determination of an analytic completion, bounded in modulus for each channel,
• Rational approximation of fixed McMillan degree,
• Determination of a constrained realization.
RARL2
Réalisation interne et Approximation Rationnelle L2
Scientific Description
The method is a steepestdescent algorithm. A parametrization of MIMO systems is used, which ensures that the stability constraint on the approximant is met. The implementation, in Matlab, is based on statespace representations.
RARL2 performs the rational approximation step in the software tools PRESTOHF and FindSources3D. It is distributed under a particular license, allowing unlimited usage for academic research purposes. It was released to the universities of Delft and Maastricht (the Netherlands), Cork (Ireland), Brussels (Belgium), Macao (China) and BITSPilani Hyderabad Campus (India).
Functional Description
RARL2 is a software for rational approximation. It computes a stable rational L2approximation of specified order to a given L2stable (L2 on the unit circle, analytic in the complement of the unit disk) matrixvalued function. This can be the transfer function of a multivariable discretetime stable system. RARL2 takes as input either:
• its internal realization,
• its first N Fourier coefficients,
• discretized (uniformly distributed) values on the circle. In this case, a leastsquare criterion is used instead of the L2 norm.
It thus performs model reduction in the first or the second case, and leans on frequency data identification in the third. For bandlimited frequency data, it could be necessary to infer the behavior of the system outside the bandwidth before performing rational approximation.
An appropriate Möbius transformation allows to use the software for continuoustime systems as well.
Sollya
Keywords: Numerical algorithm  Supremum norm  Curve plotting  Remez algorithm  Code generator  Proof synthesis
Functional Description
Sollya is an interactive tool where the developers of mathematical floatingpoint libraries (libm) can experiment before actually developing code. The environment is safe with respect to floatingpoint errors, i.e. the user precisely knows when rounding errors or approximation errors happen, and rigorous bounds are always provided for these errors.
Among other features, it offers a fast Remez algorithm for computing polynomial approximations of real functions and also an algorithm for finding good polynomial approximants with floatingpoint coefficients to any real function. As well, it provides algorithms for the certification of numerical codes, such as Taylor Models, interval arithmetic or certified supremum norms.
It is available as a free software under the CeCILLC license.