Section 0: Introduction

In this page, no information is provided about multiexpFD, the graphic user interface for moments. Only the text-based version of the program is described. This is because a GUI should not require any explanation.

Section 1: Installation

Section 2: Running moments

  1. Write a file with instructions for creating fcn (see section 3)
  2. run:
    moments fcn_file_name [options]
  3. see the results
The file fcn_file_name can be the same used for multiexp, and also the output files are the same. The options are described in section 4. As a general rule, time scales are relative; use always the same time unit (ps for example).

Section 3: FCN file

This file defines the experimental data that we want to analyze. It is made by a sequence of commands. More than one command can be put on a same line, by separating them with a ";". Lines beginning with "#" are considered comments; the text is copied to the stdout when the file is read, and is not processed.
The command can be any of the following.
scale = scale_value
where scale_value is the distance (in ps) from consecutive bins. For example:
scale = 2.44
  • maxdelta = max_delta_value
    The F can be displaced with respect to its IRF. The program looks for the best fit displacing the functions by an amount δ, less than max_delta_value in ps.
  • lambda_corr λ0 c0 c1 c2 ...
    The measured amplitude can be dependent on wave length λ. lambda_corr defines a correction for this. The amplitude will be multiplied by:
    c0 + c1(λ-λ0) + c2*(λ-λ0)2 + ...
    save data "filename"
    The program can output some data on a file. Writing to files is performed when the user calls the standard command at the minuit prompt. But the definition of the file names must be performed in FCN file. data can be graph, tau, gpfile. By default, files are not saved; they are not saved also if file name is a null string "". graph generates a file with one block for each F, with four columns: λ, F value, best fit, IRF. tau contains all the parameter values. gpfile is a gnuplot command file, that can read "tau" and generate a graph with the DAS.
    load decay "filename" [ (from-to) ] lambda time
    load IRF "filename" [ (from-to) ]
    These commands load the F and the IRF. Since each decay can have a different IRF, a load IRF command must be issued before all the load decay" that have that IRF. For example:
    load IRF "irfA.txt"
    load decay "decay1_irfA.txt" 650 100
    load decay "decay2_irfA.txt" 670 100
    load decay "decay3_irfA.txt" 690 100
    load IRF "irfB.txt"
    load decay "decay1_irfB.txt" 650 100
    load decay "decay2_irfB.txt" 670 100
    load decay "decay3_irfB.txt" 690 100

    The first group of decays has been measured with a given setup, and its IRF has been saved as "irfA.txt". Then, a second group of measures has been performed, with a different setup, and its IRF has been saved as "irfB.txt".

    The (from-to) can be optionally appended to the command, in order to define which lines must be processed.

    For "decay" measurements, "lambda" and "time" must be defined. "lambda" will be used for lambda_corr (if any), while "time" will be used to normalize the resulting A.

    The files with data must contain a column of numbers, representin the counts in each bin. Negative values are excluded from the fit. It's worth noting that a poissonian error is assumed for every count in a bin, and is evaluated as the square root of the counts. So do not normalize or multiply the counts by any amount.

    basename "base_name"
    has effect on all the subsequent load commands. It adds a base name to the file name. For example:
    basename "data/"
    load decay "d1.txt" 680 10
    loads the file "data/d1.txt". This command can be issued anywhere; it has effect until another basename command is issued. To stop the effect of a basename command, use basename ""
    Note: the file names can contain any character different from ". If you want to use the character ", you must type it twice. Example:
    load decay "test"".txt" 680 10

    Section 4: Options

    Moment method requires only a few amount of control parameters. Basically, only the number of τs must be provided by the user. Other parameters can be provided, if necessary: moment index displacement, the τ of the reference decay (IRF), the time constant for exponential depression. All the parameters must be provided by options in the command line:
    -nu N
    use N decays (default: 1)
    -displ N
    moment index displacement = N (default: 0)
    -tauR t
    decay time of the reference = t (default: no correction)
    -depr t
    exponential depression with time constant = t
    moments can scan a range of values of parameters, and put all the results in the output table. All the four parameter can be changed into parameter ranges:
    -Inu Nmin Nmax Nstep
    -Idispl Nmin Nmax Nstep
    -ItauR tmin tmax tstep
    -Idepr tmin tmax tstep
    For example:

    moments fit.fcn -nu 3 -displ 1 -tauR 32.1 -Idepr 200 3000 100

    calculates three τ, with moment index displacement 1, correcting for the decay of the IRF with τR = 32.1ps, and scans the values of the time constant of the exponential depression in the range from 200ps to 3000ps, with steps of 100ps.