Update quickstart tutorial

Jürgen Knödlseder
1 parent 1ae5c76b
Showing 1 changed file with 39 additions and 17 deletions
doc/source/user_manual/getting_started/quickstart.rst
@@ -336,8 +336,8 @@ and we do the fit by typing:
  
   $ ctlike
   Event list, counts cube or observation definition file [events.fits] cntcube.fits
-  Exposure cube file [NONE] 
-  PSF cube file [NONE] 
+  Exposure cube file (only needed for stacked analysis) [NONE] 
+  PSF cube file (only needed for stacked analysis) [NONE] 
   Calibration database [dummy] 
   Instrument response function [cta_dummy_irf] 
   Source model [$CTOOLS/share/models/crab.xml] 
@@ -361,7 +361,7 @@ the XML result file that has been produced by the run:
  
   <?xml version="1.0" encoding="UTF-8" standalone="no"?>
   <source_library title="source library">
-    <source name="Crab" type="PointSource" tscalc="0">
+    <source name="Crab" type="PointSource">
       <spectrum type="PowerLaw">
         <parameter name="Prefactor" value="6.07928" error="0.204582" scale="1e-16" min="1e-07" max="1000" free="1" />
         <parameter name="Index" value="2.5009" error="0.0252057" scale="-1" min="0" max="5" free="1" />
@@ -387,20 +387,6 @@ Crab as well as the ``Normalization`` and ``Sigma`` parameter of the radial
 acceptance model have been fitted (all parameters having the attribute 
 ``free="1"`` are fitted).
  
-.. note::
-
-   You may have noticed that the Crab source contains an additional
-   ``tscalc`` attribute in the XML result file. This attribute can be
-   used to instruct :ref:`ctlike` to compute the Test Statistics
-   (which is a measure of the detection significance) of the source.
-   To do so, add ``tscalc="1"`` to the XML file on input
-   and then re-run :ref:`ctlike`. This will then give the following result:
-
-   .. code-block:: xml
-
-      <source name="Crab" type="PointSource" ts="6875.350" tscalc="1">
-
-
 To get more details about the model fitting you can inspect the log file.
 Below the last lines of the ctlike.log log file that has been produced by
 this run:
@@ -490,6 +476,42 @@ are not too far of the best fitting values).
    then free some of the model parameters so that the fit can correctly
    describe the data.
  
+.. note::
+
+   The :ref:`ctlike` tool has the ability to estimate the detection 
+   significance for sources in the XML model. This is done by computing
+   the Test Statistic value which is defined as twice the log-likelihood
+   difference between fitting a source at a given position on top of a 
+   (background) model or fitting no source. Roughly speaken, the square
+   root of the Test Statistic value gives the source detection significance
+   in Gaussian sigmas, although the exact relation depends somewhat on
+   the formulation of the statistical problem.
+
+   To instruct :ref:`ctlike` to compute the Test Statistic value for a
+   given source you need to add the attribute ``tscalc="1"`` to the XML
+   file:
+
+   .. code-block:: xml
+
+      <source name="Crab" type="PointSource" tscalc="1">
+
+   :ref:`ctlike` will then compute the Test Statistic value for that
+   source and dump the result in the log file:
+
+   .. code-block:: xml
+
+      2015-02-05T08:29:07: === GModelSky ===
+      2015-02-05T08:29:07:  Name ......................: Crab
+      2015-02-05T08:29:07:  Instruments ...............: all
+      2015-02-05T08:29:07:  Test Statistic ............: 6875.35
+
+   The Test Statistic value will also be added as new attribute
+   ``ts`` to the XML result file:
+
+   .. code-block:: xml
+
+      <source name="Crab" type="PointSource" ts="6875.350" tscalc="1">
+
  
 .. _sec_unbinned_cta: