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12	<P>
13	<IMG SRC="../icons/g4_small.gif" WIDTH="312" HEIGHT="76">
14	</P>
15	</DIV><DIV ALIGN="center"> <H1>Frequently Asked Questions</H1><H1> </H1></DIV>
16	<P>
17	<P>
18	<P>
19
20	<UL>
21	<LI> <B><A NAME="q-general"></A><A HREF="#a-general">General</A></B>
22	<OL>
23	<LI><A HREF="#gen-1">How do I add a FAQ to this page?</A></LI>
24	</OL>
25	</LI>
26	<BLOCKQUOTE>
27	<P>  </P>
28	</BLOCKQUOTE>
29	<LI><B><A NAME="q-install"></A><A HREF="#a-install">Installation</A></B>
30	<OL>
31	<LI><A HREF="#install-1">When I download the source from the web, and unpack
32	the tar file, some files unpack into the top level directory.</A> </LI>
33	<LI><A HREF="#install-2">I cannot find CLHEP files or library and I have it
34	installed in my system</A>. </LI>
35	<LI><a href="#install-3">I installed CLHEP and the "Hist"
36	package for histogramming is missing. Where can I find it and how can
37	I do for making histograms.</a> </LI>
38	<LI><a href="#install-4">While installing the Geant4 libraries I get the
39	following message printed:</a><br>
40	<code>         gmake[1]: cernlib:
41	Command not found</code> <br>
42	<a href="#install-4">Has Geant4 been installed properly ? What to do to
43	solve this error ? </a> </LI>
44	<LI><a href="#install-5">Trying building the Geant4 libraries I see several
45	of these errors appearing and my installation fails:</a><br>
46	<code>          .....G4Exception.d:1:
47	*** missing separator. Stop.<br>
48	</code><code>...../G4DalitzDecayChannel.d:1:
49	*** missing separator. Stop. <br>
50	:<br>
51	: </code>
52	<br>
53	<a href="#install-5">Has Geant4 been installed properly ? What to do to
54	solve this error ? </a> </LI>
55	<LI><a href="#install-6">I'm trying to build Geant4 on Linux Red-Hat
56	7.0/7.1 with gcc-2.96.XX and get errors in compilation or when building
57	the file dependencies.</a> </LI>
58	<LI><a href="#install-7">Trying to install Geant4 on Linux with gcc-3.X
59	compiler, I get compilation errors from CLHEP/DRand48Engine. </a> </LI>
60	</OL>
61	</LI>
62	<BLOCKQUOTE>
63	<P>  </P>
64	</BLOCKQUOTE>
65	<LI><B><A NAME="q-run"></A><A HREF="#a-run">Runtime Problems</A></B>
66	<OL>
67	<LI><A HREF="#runtime-1">On Linux Red-Hat 6.1, I get a segmentation fault
68	as soon as I run one of the official extended examples. I also noticed
69	that random engine status is not stored on file.</A>
70	</LI>
71	<LI><a href="#runtime-2">I installed Geant4 libraries and built my application,
72	when I try to run it I get:</a><br>
73	<code>
74
75	error in loading shared libraries:<br>
76
77	libCLHEP.so: cannot open shared object file:<br>
78
79	No such file or directory</code>.
80	</LI>
81	<LI><A HREF="#runtime-3">On my system I get a Floating Point Exception
82	(FPE) since some physics processes sometimes return DBL_MAX as interaction
83	length and this number is afterwards multiplied by a number greater than
84	1.</A>
85	</LI>
86	</OL>
87	</LI>
88	<BLOCKQUOTE>
89	<P>  </P>
90	</BLOCKQUOTE>
91	<LI><A NAME="q-geometry"></A><B><A HREF="#a-geometry">Geometry</A></B>
92	<OL>
93	<LI><A HREF="#a-geom-1">I have a generic point and I would like to know
94	in which physical volume I'm located in my detector geometry.</A></LI>
95	<LI><A HREF="#a-geom-2">How can I access the daughter volumes of a specific
96	physical volume?</A></LI>
97	<LI><A HREF="#a-geom-3">How can I identify the exact copy-number of a specific
98	physical volume in my mass geometry? I tried with <code>GetCopyNo()</code>
99	from my physical volume pointer, but it doesn't seem to work!</A></LI>
100	<LI><A HREF="#a-geom-4">How can I determine the exact position in global coordinates
101	in my mass geometry during tracking and how can I convert it to coordinates local to
102	the current volume ?</A></LI>
103	</OL>
104	</LI>
105	<BLOCKQUOTE>
106	<P>  </P>
107	</BLOCKQUOTE>
108	<LI><B><A NAME="q-phys"></A><A HREF="#a-phys">Physics and cuts</A></B>
109	<OL>
110	<LI><A HREF="#PHYS-1">How do production cuts (in range) work in Geant4 ?
111	Are they also used in tracking ? If a particle has an energy lower than the
112	converted cut in energy for the given material and the distance to the next
113	boundary is smaller than the cut in range, is the particle killed ?</A>
114	</OL>
115	</LI>
116	<BLOCKQUOTE>
117	<P>  </P>
118	</BLOCKQUOTE>
119	<LI><B><A NAME="q-vis"></A><A HREF="#a-vis">Visualization</A></B>
120	<OL>
121	<LI><A HREF="#VIS-1">I have set G4VIS... environmental variables but visualization
122	does not appear to be enabled.</A>
123	<LI><A HREF="#VIS-2">Geant4 crashes while trying to open an OpenGLX window.</A>
124	</OL>
125	</LI>
126	</UL>
127
128	<HR>
129
130	<H3><A NAME="a-general"></A><A HREF="#q-general">General</A></H3>
131	<OL>
132	<LI><A NAME="gen-1"></A><I>How do I add a FAQ to this page?</I>
133	<BR><BR>
134	<I>Solution:</I><BR>
135	This is done manually at the moment. Please send your FAQ with solution
136	to the <A HREF="mailto:Gunter.Folger@cern.ch, Gabriele.Cosmo@cern.ch">editors</A>.
137	</LI>
138	</OL>
139
140	<HR>
141
142	<H3> <A NAME="a-install"></A><A HREF="#q-install">Installation</A> </H3>
143	<OL>
144	<LI><A NAME="install-1"></A><I>When I download the source from the web, and unpack
145	the tar file, some files unpack into the top level directory.</I><BR>
146	<BR>
147	<I>Solution:</I><BR>
148	The problem you describe usually is the result of using "UNIX" tar to
149	unpack the gtar ("GNU-tar") file, or vice versa, or using zip on either the
150	gtar or tar file. Please make certain that you download the correct file for
151	your system, and that you use the correct unpacking tool. Note that for Linux
152	you must download the gtar.gz file.<P>
153	</LI>
154	<LI><A NAME="install-2"></A><I>I cannot find CLHEP files or library and I have
155	it installed in my system.</I><BR>
156	<BR>
157	<I>Solution:</I><BR>
158	If the standard CLHEP installation procedure has been adopted, the variable
159	$CLHEP_BASE_DIR should point to the area where include/ and lib/ directories
160	for CLHEP headers & lib are installed (i.e., it should be /usr/local for the
161	default CLHEP installation). In case the library name is different than the
162	one expected (libCLHEP.a), you should either create a symbolic link with the
163	expected name, or define the variable CLHEP_LIB in your environment which
164	explicitly sets the name of the CLHEP library. If a non-standard CLHEP installation
165	has been adopted, define variables $CLHEP_INCLUDE_DIR, $CLHEP_LIB_DIR (and
166	$CLHEP_LIB) to refer explicitly to the place where includes, library (and
167	library-name) respectively are placed in your system.<P>
168	</LI>
169	<li><a name="install-3"></a><i>I installed </i>CLHEP<i> and the
170	"</i>Hist<i>" package for histogramming is missing. Where can I find it and
171	how can I do for making histograms.</i><br>
172	<br>
173	<i>Solution:</i><br>
174	In Geant4, histogramming is done through the standard AIDA interface;
175	these histograms can be displayed or otherwise manipulated using analysis
176	tools based on the AIDA interface (JAS, Lizard, Open Scientist, ...). Examples
177	are shown in examples/extended/analysis and examples/advanced applications.
178	<br>
179	<br>
180	The obsolete and no-longer maintened "Hist" module can be downloaded from
181	the <a href="http://pcitapiww.cern.ch/asd/lhc++/INSTALLATION/clhep-1.5.html">
182	CLHEP 1.5 distribution from web</a>, but requires some modifications to the
183	CLHEP installation scripts to be properly installed.<P>
184	</li>
185	<li><a name="install-4"></a><i>While installing the Geant4 libraries I get
186	the following message printed:</i><br>
187
188	gmake[1]: cernlib: Command not found <br>
189	<i>Has Geant4 been installed properly ? What to do to solve this error ?</i><br>
190	<br>
191	<i>Solution:</i><br>
192	The message:<br>
193	<code>
194	gmake[1]: cernlib: Command not found
195	</code> <br>
196	shows that you don't have the 'cernlib' command installed in your system;
197	'cernlib' is a command from the CERN program library (cernlib) returning a
198	list of libraries needed to link a cernlib application. This command is only
199	used in the 'g3tog4' module, however, if you do not make use of the 'g3tog4'
200	tool, it's harmless. The cernlib script (and the needed cernlib libraries)
201	are available from: <a href="http://cern.ch/cernlib">http://cern.ch/cernlib</a>.<P>
202	</li>
203	<li><a name="install-5"></a> <i>Trying building the Geant4 libraries I see several
204	of these errors appearing and my installation fails:</i><br>
205	<code>
206	.....G4Exception.d:1:
207	*** missing separator. Stop.<br>
208
209	...../G4DalitzDecayChannel.d:1:
210	*** missing separator. Stop. <br>
211
212	:<br>
213
214	:
215	</code> <br>
216	<i>Has Geant4 been installed properly ? What to do to solve this error ?</i><br>
217	<br>
218	<i>Solution:</i><br>
219	It looks like some file dependencies (.d) are corrupted, possibly
220	due to previous build attempts which failed for some reason.<br>
221	You need to remove each of them; you can use:
222	<pre>
223	gmake dependencies='' clean
224	</pre>
225	from the affected module (i.e. for this case, from
226	$G4INSTALL/source/global/management and
227	$G4INSTALL/source/particles/management)
228	and rebuild.
229	<br>Alternatively, you may use:
230	<pre>
231	gmake clean
232	</pre>
233	from geant4/source and rebuild.<P>
234	</li>
235	<li><a name="install-6"></a><i>I'm trying to build Geant4 on Linux Red-Hat
236	7.0/7.1 with gcc-2.96.XX and get errors in compilation or when building
237	the file dependencies.</i><br>
238	<br>
239	<i>Solution:</i><br>
240	Geant4 is supported on Red Hat 6.1 with gcc-2.95.2. Moreover, note
241	that on versions 7.X, Red Hat Linux is distributed with a flawed version of
242	the gcc compiler which has -never- been officially released by GNU. The compiler
243	gcc-2.96.XX may require strict ISO/ANSI setup. If so the following changes
244	in Geant4 3.2 may help to build most of the modules in Geant4, although we
245	cannot guarantee a correct behavior of a program built with such compiler.
246	In geant4/config/sys/Linux-g++.gmk modify the line:<br>
247	<code>      CXXFLAGS := -pipe -fno-for-scope -DGNU_GCC</code><br>
248	to<br>
249	<code>     CXXFLAGS := -ansi -pedantic -pipe -fno-for-scope
250	-DGNU_GCC</code><br>
251	<br>
252	And the following lines:<br>
253	<code>     </code><code>ifdef G4USE_OSPACE<br>
254	CPPFLAGS += -DOS_LINUX_2 -DOS_NEW_CHECK -DOS_STL_ASSERT<br>
255	CPPFLAGS += -DOS_NO_WSTRING -DOS_NO_ALLOCATORS<br>
256	CPPFLAGS += -I$(OSPACE_BASE_DIR)/ospace/std
257	-I$(OSPACE_BASE_DIR)<br>
258	# else<br>
259	# G4USE_STD_NAMESPACE := yes<br>
260	# CPPFLAGS += -DG4USE_STD_NAMESPACE<br>
261	endif</code><br>
262	to:<br>
263	<code>     </code><code>G4USE_STD_NAMESPACE := yes<br>
264	CPPFLAGS += -DG4USE_STD_NAMESPACE</code><br>
265	<br>
266	Rebuild from scratch:<br>
267	<code>     </code> <code>cd geant4/source<br>
268	gmake clean<br>
269	gmake<br>
270	</code><P>
271	</li>
272	<li><a name="install-7"></a><i>Trying to install Geant4 on Linux with gcc-3.X
273	compiler, I get compilation errors from CLHEP/DRand48Engine.</i><br>
274	<br>
275	<i>Solution:</i><br>
276	To overcome this problem on gcc-3.X, you should reinstall CLHEP and
277	comment out or remove the lines included between <br>
278	<code>
279	#if !defined(__GNUC__) \|\| defined(__STRICT_ANSI__) <BR>
280	... <BR>
281	#endif <br></code>
282	in DRand48Engine.h. <br>
283	This problem is fixed in a higher (>1.7) version of the CLHEP package.
284	</li>
285	</ol>
286
287	<HR>
288
289	<H3><A NAME="a-run"></A><A HREF="#q-run">Run Time Problems</A> </H3>
290	<OL>
291	<LI><A NAME="runtime-1"></A><I>On Linux Red-Hat 6.1, I get a segmentation fault
292	as soon as I run one of the official extended examples. I also noticed that
293	random engine status is not stored on file.</I><BR>
294	<BR>
295	<I>Solution:</I><BR>
296	Check that the CLHEP library has been installed and compiled with Red-Hat
297	6.1. A binary object produced with Red-Hat 5.X is not fully compatible with
298	binaries running on RH 6.X, due to a different libc used in the two configurations.<P>
299	</li>
300	<li><a name="runtime-2"></a><i>I installed Geant4 libraries and built my application,
301	when I try to run it I get:</i><br>
302	<code>
303
304	error in loading shared libraries:<br>
305
306	libCLHEP.so: cannot open shared object file:<br>
307
308	No such file or directory.
309	</code><br>
310	<br>
311	<i>Solution:</i><br>
312	Your installation of CLHEP includes shared libraries. You need to specify
313	the path where libCLHEP.so is installed through your environment variable
314	LD_LIBRARY_PATH.<P>
315	</li>
316	<LI><A NAME="runtime-3"></A><I>On my system I get a Floating Point Exception
317	(FPE) since some physics processes sometimes return </I>DBL_MAX<I> as interaction
318	length and this number is afterwards multiplied by a number greater than 1.</I><BR>
319	<BR>
320	<I>Solution:</I><BR>
321	Geant4 coding conventions and installation setup explicitly follow the ANSI/IEEE-754
322	Standard for the initialization of floating-point arithmetic hardware and
323	portability. The Standard foresees floating-point arithmetic to be nonstop
324	and underflows to be gradual. On DEC platforms, for example, the ANSI/IEEE-754
325	Standard compliance needs to be explicitly set (since deactivated by default);
326	in this case we use infact the option "-ieee" on the DEC/cxx native C++ compiler
327	to achieve this. You should check if your compiler provides compilation options
328	for activating Standard initialization of FP arithmetic (it may be platform
329	specific).
330	</LI>
331	</OL>
332
333	<HR>
334
335	<H3><A NAME="a-geometry"></A><A HREF="#q-geometry">Geometry</A> </H3>
336	<OL>
337	<LI><A NAME="a-geom-1"></A><I>I have a generic point and I would like to know
338	in which physical volume I'm located in my detector geometry.</I>
339	<BR><BR>
340	<I>Solution:</I><BR>
341	The best way of doing this is by invoking the G4Navigator. First get a pointer
342	of the navigator through the G4TransportationManager, and then locate the point.
343	i.e.
344	<pre>
345	#include "G4TransportationManager.hh"
346	#include "G4Navigator.hh"
347	G4ThreeVector myPoint = ....;
348	G4Navigator* theNavigator = G4TransportationManager::GetTransportationManager()->GetNavigatorForTracking();
349	G4VPhysicalVolume* myVolume = theNavigator->LocateGlobalPointAndSetup(myPoint);
350	</pre>
351	</LI>
352	<LI><A NAME="a-geom-2"></A><I>How can I access the daughter volumes of a specific
353	physical volume?</I>
354	<BR><BR>
355	<I>Solution:</I><BR>
356	Through the associated logical volume.
357	<pre>
358	G4VPhysicalVolume* myPVolume = ....;
359	G4LogicalVolume* myLVolume = myPVolume->GetLogicalVolume();
360	for (G4int i=0; i<myLVolume->GetNoDaughters(); i++)
361	myPVolume = myLVolume->GetDaughter(i);
362	</pre>
363	</LI>
364	<LI><A NAME="a-geom-3"></A><I>How can I identify the exact copy-number of a specific
365	physical volume in my mass geometry? I tried with <code>GetCopyNo()</code>
366	from my physical volume pointer, but it doesn't seem to work!</I>
367	<BR><BR>
368	<I>Solution:</I><BR>
369	The correct way to identify -uniquely- a physical volume in your
370	mass geometry is by using the touchables (see also section 4.1.5 of the
371	User's Guide for Application Developers), as follows:
372	<pre>
373	G4Step* aStep = ..;
374	G4StepPoint* preStepPoint = aStep->GetPreStepPoint();
375	G4TouchableHandle theTouchable = preStepPoint->GetTouchableHandle();
376	G4int copyNo = theTouchable->GetReplicaNumber();
377	G4int motherCopyNo = theTouchable->GetReplicaNumber(1);
378	</pre>
379	where <code>Replica</code> here stays for any duplicated instance of a physical
380	volume, either if it is a <code>G4PVPlacement</code> (multiple placements of the
381	same logical volume) or a <code>G4PVReplica</code>/<code>G4PVParameterised</code>.<BR>
382	The method <code>GetCopyNo()</code> is meant to return only the serial
383	number of placements not duplicated in the geometry tree.<P>
384	</LI>
385	<LI><A NAME="a-geom-4"></A><I>How can I determine the exact position in global coordinates
386	in my mass geometry during tracking and how can I convert it to coordinates local to
387	the current volume ?</I>
388	<BR><BR>
389	<I>Solution:</I><BR>
390	You need again to do it through the touchables (see also section 4.1.5 of the
391	User's Guide for Application Developers), as follows:
392	<pre>
393	G4Step* aStep = ..;
394	G4StepPoint* preStepPoint = aStep->GetPreStepPoint();
395	G4TouchableHandle theTouchable = preStepPoint->GetTouchableHandle();
396	G4ThreeVector worldPosition = preStepPoint->GetPosition();
397	G4ThreeVector localPosition = theTouchable->GetHistory()->
398	GetTopTransform().TransformPoint(worldPosition);
399	</pre>
400	where <code>worldPosition</code> here stays for the position related to the world
401	volume, while <code>localPosition</code> refers to the coordinates local to the
402	volume where the particle is currently placed.
403	</LI>
404	</OL>
405
406	<HR>
407
408	<H3><A NAME="a-phys"></A><A HREF="#q-phys">Physics and cuts</A> </H3>
409	<OL>
410	<LI><I><A NAME="PHYS-1"></A>How do production cuts (in range) work in Geant4 ?
411	Are they also used in tracking ? If a particle has an energy lower than the
412	converted cut in energy for the given material and the distance to the next
413	boundary is smaller than the cut in range, is the particle killed ?</I>
414	<BR><BR>
415	<I>Answer:</I><BR>
416	Geant4 does NOT have a "tracking cut". The toolkit's default behaviour
417	is to track particles down to zero range (i.e. zero energy).<BR>
418	Of course, it is possible for the user to create and register a process
419	that kills particles below a certain energy or range; this is however
420	NOT provided by default in Geant4. So there's NO "tracking cut".<BR>
421	For example, suppose a particle that is nearing zero energy will at some point
422	be proposed by its Ionisation process to undergo one final step, from its current
423	energy down to zero energy. This is still only a proposal. If during this step
424	the particle crosses a boundary, then the transportation will limit the step at
425	a length smaller than the Ionisation -- so the particle will still see and cross
426	the relevant boundary, and another step will occur on the other side of that
427	boundary.<BR>
428	In summary the "production threshold" range and its equivalent in
429	energy are not utilised as a "tracking cut". A particle is not abandoned
430	by Geant4 below a certain range/energy unless the user registers a process
431	to do this by him/her-self.
432	</LI>
433	</OL>
434
435	<HR>
436
437	<H3><A NAME="a-vis"></A><A HREF="#q-vis">Visualization</A> </H3>
438	<OL>
439	<LI><I><A NAME="VIS-1"></A>I have set G4VIS... environmental variables but visualization
440	does not appear to be enabled.</I>
441	<BR><BR>
442	<I>Solution:</I><BR>
443	This might be
444	because you set the environment variables after already compiling. The environment
445	variables control C-pre-processor macros of the same name and therefore influence
446	what code gets compiled. I suggest: (setenv or export the environment variables)
447	<PRE>
448	cd $G4INSTALL/source/visualization
449	gmake clean
450	gmake
451	cd $G4INSTALL/source/interfaces
452	gmake clean
453	gmake
454	cd $G4INSTALL/source
455	gmake libmap
456	cd [your working directory]
457	gmake clean
458	gmake
459	</PRE>
460	Try environment variables <CODE>G4VIS_BUILD_xxx_DRIVER</CODE>
461	and <CODE>G4VIS_USE_xxx</CODE>, where xxx = <CODE>OPENGLX, DAWN, DANWFILE, VRML,
462	VRMLFILE</CODE> all set to 1.<P>
463	</LI>
464	<LI><I><A NAME="VIS-2"></A>Geant4 crashes while trying to open an OpenGLX window.</I>
465	<BR><BR>
466	<I>Solution:</I><BR>
467	This might be because you are using Mesa-3.1. Mesa-3.0 works.
468	</LI>
469	</OL>
470
471	<HR>
472	Wednesday, 21 May 2003 -
473	<I> <A HREF="http://consult.cern.ch/xwho/people/20341">GC</A>,
474	<A HREF="http://consult.cern.ch/xwho/people/1342">GF</A>
475	</I>
476	</BODY>
477	</HTML>

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