How to Get the LEVM/LEVMW Version 8.08
Complex Nonlinear Least Squares Fitting Program
The current revision of the CNLS frequency-response fitting software, LEVM/LEVMW, V.8.08, is now available (March 2007) at no cost, from Solartron Analytical. It includes both the LEVM program files for MS-DOS and the new LEVMW files for full operation in WINDOWS.
You can download the full program files and the manual (in WORD or PDF) from the Solartron website. Click on the Solartron link here. You will need to register with them before you can download the software. After registration you will receive a password and a username by email. They will be generated automatically and should arrive within a few hours. These must be used to access the download section of the SolartronAnalytical website. The login and password, however, will not be activated until they have been approved by a person, which may take up 24 hours during business hours.
Install the download to a temporary empty directory. The material is provided in compressed form. It is particularly important to print the entire manual before beginning work with LEVM/LEVMW. The first six pages of the manual provide valuable information about LEVMW and how to start to use it immediately. If you experience a problem downloading the LEVM/LEVMW material, please send me an email message.
The full program material involves a total of about 6 MB of files or more, and the 160-page manual, which is essential. LEVMW runs directly on a PC under WINDOWS. LEVM requires either MS-DOS, or the MS-DOS mode of WINDOWS, and all its FORTRAN source code is included, along with an executable version, so the program may be compiled for any other machine or operating system.
In addition to providing a very powerful complex nonlinear least squares (CNLS) procedure for fitting small-signal frequency response data, LEVM/LEVMW also allows transient data to be fit to a model; it also includes provision for solving the inverse problem of estimating the distribution of the relaxation times function present from either type of data; and it can be used for measurement-model analysis and as a way of verifying that data satisfy the Kronig-Kramers transform relations, one superior to, and simpler than, direct KK integral transformation.
The LEVM program can be recompiled to use any fitting model which can be mathematically specified, for any number of data points (within the limitation of available memory). This is not usually necessary since the current version of the program allows fitting to many thousands of equivalent circuits which may involve more than 35 different distributed circuit elements. More description of an earlier version of LEVM appears in Solid State Ionics 23(1987)61. It has been very much improved and updated since then. The present LEVMW and LEVM versions 8.08 are much more general, versatile, and powerful than any other CNLS program that I know of and are a big improvement over earlier versions of LEVM.
If you get and use LEVMW/LEVM, I believe you will find it to be very helpful. I am still involved with the program and would be interested in hearing of your experience with it. In particular, please notify me by email of any bugs you may discover. Best of luck.
For further Solartron information contact:
SOLARTRON ANALYTICAL, Unit B1, Armstrong Mall
e-mail: info@solartronanalytical.com
Farnborough, Hampshire
GU14 ONR
ENGLAND
Phone: +44 1252 556800; FAX: +44 1252 556899.
SOME FEATURES OF CNLS PROGRAM LEVMW/LEVM
- Millions of built-in circuit possibilities available. New fitting models can be easily added since all source code is included.
- > 10 different weighting choices are available, and weighting parameters may be free parameters of the fit
- > about 37 different distributed circuit elements (DCE's) available for circuits
- Complex-, real-, or imaginary-part fitting is possible
- A complex-fit optimization procedure is available
- Input data may be in Z, Y, E (complex epsilon), or M form
- Fitting or simulation may be at Z, Y, E, or M level
- Input/output may be in rectangular, polar, or log-polar form
- Applicable for conductive, dielectric, or mixed systems, including semiconductors, electrolytes, polymers, etc. Allows simultaneous fitting of data involving separate conductive-system and dielectric-system dispersions
- Fitting of transient-response data is possible for many response models
- Powerful 2- and 3-D plotting program included and a direct Windows graphics program
- Subtraction of the effects of selected circuit elements possible
- "Measurement-model" fitting and Kronig-Kramers testing available
- Estimation of distributions is possible by powerful methods of inversion of frequency or transient response data. This allows accurate transformation of wide-range data from time-to-frequency or vice versa without the need for Fourier transformation
- Two types of conductive-system dispersion models available for fitting
- Accurate stretched-exponential (KWW) fitting model included
- New generalized-exponential-distribution fitting model available
- Many of the fitting models may be used with or without adjustable small-tau cutoff of the distribution of relaxation times (tau) associated with the response, and the cutoff point may be a free parameter of the fit
Ross Macdonald