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*Subject*: Re: Question about tutorial in 1D Gaussian Filter*From*: Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>*Date*: 30 Jul 2001 16:56:30 -0500*Newsgroups*: comp.lang.idl-pvwave*Organization*: U. Wisc. Madison Physics -- Compact Objects*References*: <b19810c5.0107292330.37dd66aa@posting.google.com>*Reply-To*: craigmnet(at)cow.physics.wisc.edu*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:25905

coraluk@hkpc.org (Cora) writes: > I want to use a 1D Gaussian Filter to fit a curve. After visiting the > tutorial about 1D Curve fitting in IDL, I still found some problems in > the function gauss1. Following are the questions: > > 1) What is the return of "size(x)"? > > 2) What is meant by "!dpi"? Cora, GAUSS1 is my program, so perhaps I should respond. I should be clear first of all, that computing the gaussian *should* be as simple as EXP(-Z^2/2). Unfortunately, the exponential function is sensitive to underflow warnings. If Z is too large, then EXP(-Z^2/2) will underflow. My personal wish is that this would yield zero silently, but that is not what happens. All of the code you see in GAUSS1 is designed to avoid the warning, but maintain as much precision as possible. The SIZE function is used to determine the dimension and data type of a variable. I use it that function to decide whether the data is FLOAT or DOUBLE. You can look up !DPI in the manual under system variables. If you like, a function like the following one may be easier to understand, but will produce underflow warnings: FUNCTION SIMPLEGAUSS, X, P return, P(2)*EXP(-(X-P(0))^2/(2.*P(1)^2)) END Good luck, Craig -- -------------------------------------------------------------------------- Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response --------------------------------------------------------------------------

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