Programs in Physics & Physical Chemistry
|[Licence| Download | New Version Template] adje_v1_0.tar.gz(184 Kbytes)|
|Manuscript Title: VisRes: a GRACE tool for displaying and analysing resonances.|
|Authors: D.W. Busby, P.G. Burke, V.M. Burke, C.J. Noble, N.S. Scott|
|Program title: VisRes 2.00|
|Catalogue identifier: ADJE_v1_0|
Distribution format: tar.gz
|Journal reference: Comput. Phys. Commun. 114(1998)243|
|Programming language: C, Fortran, Motif.|
|Operating system: Solaris 2.5, IRIX5.3, HP-UX9.05, ULTRIX4.3, AIX2.3.|
|RAM: 16M words|
|Keywords: Atomic physics, Scattering, Electron, General purpose, Fit, Farm, Grace, Osf/motif, Resonance, R-matrix.|
|Classification: 2.4, 4.9.|
Nature of problem:
Electron and photon collisions with atoms and molecules give rise to quasi-bound states with long lifetimes. These resonances are exhibited in theoretical computations by a rapid increase in the eigenphase sum of approximately pi radians. VisRes is a graphical tool designed to enable the user to read files of eigenphase sums, to detect resonances, and to determine accurately their positions and widths.
Detecting and analysing resonances from a file of energy dependent eigenphase sums is difficult for two reasons. First, there are often insufficient data points in the vicinity of a resonance to determine its characteristics accurately. Second, rapid changes in an eigenphase sum can result from the transition from one arctan branch to another, rather than from a resonance. VisRes is a graphical tool designed to circumvent these difficulties. It enables files of eigenphase sums to be read and the data displayed as discontinuous graphs, over a range of pi radians, and as continuous graphs, over a range of npi radians. Additional points needed to resolve a resonance can be computed interactively by invoking FARM  or a similar program and merging the new data into the displayed graphs. Resonance positions and widths are determined by fitting interactively selected data points by the Breit- Wigner formula . The fitting is performed by the Fortran subroutine SNLS1E from the public domain SLATEC Library . It minimizes the sum of the squares of M nonlinear functions in N variables by a modification of the Levenberg-Marquardt algorithm. The SNLS1E source code is included in the VisRes code distribution.
Current array dimension settings impose the following restrictions: VisRes can deal with up to three overlaping resonances and a background polynomial phaseshift up to degree four; the maximum number of data points that can be used in the fitting process is restricted to 250; and the number of data points that can be computed interactively at one time is restricted to 25. Larger cases can be considered by altering the array dimensions.
VisRes can be operated exclusively on the host workstation or in distributed mode where data is read from and computed on a remote computer but displayed and analysed on the host workstation.
|||V.M. Burke and C.J. Noble, Comput. Phys. Commun. 85 (1995) 471.|
|||G. Breit and E.P. Wigner, Phys. Rev. 49 (1936) 519.|
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