faq.html

Libsvm is a simple, easy-to-use, and efficient software for SVM classification and regression. It c

<p>
There is absolutely no reason the probability outputs guarantee
you better accuracy. The main purpose of this option is
to provide you the probability estimates, but not to boost
prediction accuracy. From our experience, 
after proper parameter selections, in general with
and without -b have similar accuracy. Occasionally there
are some differences.
It is not recommended to compare the two under 
just a fixed parameter
set as more differences will be observed.
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<a name="f427"><b>Q: Why the code gives NaN (not a number) results?</b></a>
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<p>
This rarely happens, but few users reported the problem.
It seems that their 
computers for training libsvm have the VPN client
running. The VPN software has some bugs and causes this
problem. Please try to close or disconnect the VPN client.
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<a name="f428"><b>Q: Why on windows sometimes grid.py fails?</b></a>
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<p>
The error message is probably
<pre>
Traceback (most recent call last):
  File "grid.py", line 349, in ?
    main()
  File "grid.py", line 344, in main
    redraw(db)
  File "grid.py", line 132, in redraw
    gnuplot.write("set term windows\n")
IOError: [Errno 22] Invalid argument
</pre>

<p>There are some problems about using gnuplot on windows.
So far we have not found a good solution. 
Please try to close gnuplot windows and rerun.
If the problem still occurs, comment the following
two lines in grid.py by inserting "#" in the beginning:
<pre>
        redraw(db)
        redraw(db,1)
</pre>
Then you get accuracy only but not cross validation contours.
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  <a name="/Q5:_Graphic_Interface"></a>
<a name="f501"><b>Q: How can I save images drawn by svm-toy?</b></a>
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<p>
For Microsoft windows, first press the "print screen" key on the keyboard.
Open "Microsoft Paint" 
(included in Windows) 
and press "ctrl-v." Then you can clip
the part of picture which you want.
For X windows, you can 
use the program "xv" to grab the picture of the svm-toy window.
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<a name="f502"><b>Q: I press the "load" button to load data points but why svm-toy does not draw them ?</b></a>
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<p>
The program svm-toy assumes both attributes (i.e. x-axis and y-axis
values) are in (0,1). Hence you want to scale your 
data to between a small positive number and 
a number less than but very close to 1.
Moreover, class labels must be 1, 2, or 3
(not 1.0, 2.0 or anything else).
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<a name="f503"><b>Q: I would like svm-toy to handle more than three classes of data, what should I do ?</b></a>
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<p>
Taking windows/svm-toy.cpp as an example, you need to
modify it and  the difference
from the original file is as the following: (for five classes of
data)
<pre>
30,32c30
< 	RGB(200,0,200),
< 	RGB(0,160,0),
< 	RGB(160,0,0)
---
> 	RGB(200,0,200)
39c37
< HBRUSH brush1, brush2, brush3, brush4, brush5;
---
> HBRUSH brush1, brush2, brush3;
113,114d110
< 	brush4 = CreateSolidBrush(colors[7]);
< 	brush5 = CreateSolidBrush(colors[8]);
155,157c151
< 	else if(v==3) return brush3;
< 	else if(v==4) return brush4;
< 	else return brush5;
---
> 	else return brush3;
325d318
< 	  int colornum = 5;
327c320
< 		svm_node *x_space = new svm_node[colornum * prob.l];
---
> 		svm_node *x_space = new svm_node[3 * prob.l];
333,338c326,331
< 			x_space[colornum * i].index = 1;
< 			x_space[colornum * i].value = q->x;
< 			x_space[colornum * i + 1].index = 2;
< 			x_space[colornum * i + 1].value = q->y;
< 			x_space[colornum * i + 2].index = -1;
< 			prob.x[i] = &x_space[colornum * i];
---
> 			x_space[3 * i].index = 1;
> 			x_space[3 * i].value = q->x;
> 			x_space[3 * i + 1].index = 2;
> 			x_space[3 * i + 1].value = q->y;
> 			x_space[3 * i + 2].index = -1;
> 			prob.x[i] = &x_space[3 * i];
397c390
< 				if(current_value > 5) current_value = 1;
---
> 				if(current_value > 3) current_value = 1;
</pre>
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<a name="f601"><b>Q: What is the difference between Java version and C++ version of libsvm?</b></a>
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<p>
They are the same thing. We just rewrote the C++ code
in Java.
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<a name="f602"><b>Q: Is the Java version significantly slower than the C++ version?</b></a>
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<p>
This depends on the VM you used. We have seen good
VM which leads the Java version to be quite competitive with
the C++ code. (though still slower)
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<a name="f603"><b>Q: While training I get the following error message: java.lang.OutOfMemoryError. What is wrong?</b></a>
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<p>
You should try to increase the maximum Java heap size.
For example,
<pre>
java -Xmx256m svm_train.java ...
</pre>
sets the maximum heap size to 256M.
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<a name="f604"><b>Q: Why you have the main source file svm.m4 and then transform it to svm.java?</b></a>
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<p>
Unlike C, Java does not have a preprocessor built-in.
However,  we need some macros (see first 3 lines of svm.m4).

</ul>
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<a name="f702"><b>Q: Using python on MS windows, it fails to load the dll file.</b></a>
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<p>
It seems the dll file is version dependent. So far we haven't
found out a good solution. Please email us if you have any
good suggestions.
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<a name="f703"><b>Q: How to modify the python interface on MS windows and rebuild the dll file ?</b></a>
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<p>

To modify the interface, follow the instructions given in
<a href=http://www.swig.org/Doc1.1/HTML/Python.html#n2>
http://www.swig.org/Doc1.1/HTML/Python.html#n2</a>

<p>

If you just want to build DLL for a different python version,
after libsvm 2.5, you can easily use the file Makefile.win.
See details in README.

Alternatively, you can use Visual C++:
<ol>
<li> Create a Win32 DLL project and set (Build->Active Configuration) to "Release."
<li> Add svm.cpp, svmc_wrap.c, python2x.lib to your project.
<li> Add the directories containing Python.h and svm.h to
the Additional include directories. (in Project
Settings->C/C++->Preprocessor)
<li> add __WIN32__ to Preprocessor definitions
<li> Make sure that in the "General" category of
Project->Settings->Settings For "Win32 Release", Output
directories should be "Release"
<li> Build the DLL.
</ol>


<!--
There do exist work arounds, however. In
http://aspn.activestate.com/ASPN/Mail/Message/python-list/983252
they presented a solution: 1) find the version of python in the
registry 2) perform LoadLibrary("pythonxx.dll") and 3) resolve the
reference to functions through GetProcAddress. It is said that SWIG
may help on this.
http://mailman.cs.uchicago.edu/pipermail/swig/2001-July/002744.html
presented a similar example.
-->
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<a name="f704"><b>Q: Except the python-C++ interface provided, could I use Jython to call libsvm ?</b></a>
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<p> Yes, here are some examples:

<pre>
$ export CLASSPATH=$CLASSPATH:~/libsvm-2.4/java/libsvm.jar
$ ./jython
Jython 2.1a3 on java1.3.0 (JIT: jitc)
Type "copyright", "credits" or "license" for more information.
>>> from libsvm import *
>>> dir()
['__doc__', '__name__', 'svm', 'svm_model', 'svm_node', 'svm_parameter',
'svm_problem']
>>> x1 = [svm_node(index=1,value=1)]
>>> x2 = [svm_node(index=1,value=-1)]
>>> param = svm_parameter(svm_type=0,kernel_type=2,gamma=1,cache_size=40,eps=0.001,C=1,nr_weight=0,shrinking=1)
>>> prob = svm_problem(l=2,y=[1,-1],x=[x1,x2])
>>> model = svm.svm_train(prob,param)
*
optimization finished, #iter = 1
nu = 1.0
obj = -1.018315639346838, rho = 0.0
nSV = 2, nBSV = 2
Total nSV = 2
>>> svm.svm_predict(model,x1)
1.0
>>> svm.svm_predict(model,x2)
-1.0
>>> svm.svm_save_model("test.model",model)

</pre>

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<a name="f705"><b>Q: How could I install the python interface on Mac OS? </b></a>
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<p> According to S V N Vishwanathan in Australian National University, instead of 
LDFLAGS = -shared
in the Makefile, you need
<pre>
LDFLAGS = -bundle -flat_namespace -undefined suppress
</pre>
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  <p align="middle">
<a href="http://www.csie.ntu.edu.tw/~cjlin/libsvm">LIBSVM home page</a>
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