Support Vector Machine for Multivariate Performance Measures
Author:Thorsten Joachims <firstname.lastname@example.org>
Department of Computer Science
SVMperf is an implementation of the Support Vector Machine (SVM) formulation for optimizing multivariate performance measures described in [Joachims, 2005]. Furthermore, SVMperf implements the alternative structural formulation of the SVM optimization problem for conventional binary classification with error rate and ordinal regression described in [Joachims, 2006]. So, there are three reasons for why you might want to use SVMperf instead of SVMlight:
This implementation is an instance of SVMstruct. More information on SVMstruct is available here.
Please send me email and let me know that you got it. The archive contains the source code of the most recent version of SVMperf, which includes the source code of SVMstruct and the SVMlight quadratic optimizer. Unpack the archive using the shell command:
gunzip –c svm_perf.tar.gz | tar xvf –
makeThis will produce the executables svm_perf_learn and svm_perf_classify. If the system does not compile properly, check this FAQ.
SVMperf consists of a learning module (svm_perf_learn) and a classification module (svm_perf_classify). The classification module can be used to apply the learned model to new examples. See also the examples below for how to use svm_perf_learn and svm_perf_classify.
Usage is much like SVMlight. You call it like
svm_perf_learn -c 20.0 train.dat model.datwhich trains an SVM on the training set train.dat and outputs the learned rule to model.dat using the regularization parameter C set to 20.0. However, the interpretation of the parameter C in SVMperf is different from SVMlight. In particular, Clight = Cperf*100/n, where n is the number of training examples. Note also that the C values given in [Joachims, 2006] should be divided by 100 for equivalent results. Most of the other options come from SVMstruct and SVMlight and are described there. Only the "s
tructure learning options" listed below are particular toSVMperf.
General options: -? -> this help -v [0..3] -> verbosity level (default 1) -y [0..3] -> verbosity level for svm_light (default 0) Learning options: -c float -> C: trade-off between training error and margin (default 0.01) -p [1,2] -> L-norm to use for slack variables. Use 1 for L1-norm, use 2 for squared slacks. (default 1) -o [1,2] -> Rescaling method to use for loss. 1: slack rescaling 2: margin rescaling (default 2) -l [0..] -> Loss function to use. 0: zero/one loss (default 2) Kernel options: -t int -> type of kernel function: 0: linear (default) 1: polynomial (s a*b+c)^d 2: radial basis function exp(-gamma ||a-b||^2) 3: sigmoid tanh(s a*b + c) 4: user defined kernel from kernel.h -d int -> parameter d in polynomial kernel -g float -> parameter gamma in rbf kernel -s float -> parameter s in sigmoid/poly kernel -r float -> parameter c in sigmoid/poly kernel -u string -> parameter of user defined kernel Optimization options (see ): -q [2..] -> maximum size of QP-subproblems (default 10) -n [2..q] -> number of new variables entering the working set in each iteration (default n = q). Set nsize of cache for kernel evaluations in MB (default 40) The larger the faster... -e float -> eps: Allow that error for termination criterion (default 0.100000) -h [5..] -> number of iterations a variable needs to be optimal before considered for shrinking (default 100) -k [1..] -> number of new constraints to accumulate before recomputing the QP solution (default 100) -# int -> terminate optimization, if no progress after this number of iterations. (default 100000) Output options: -a string -> write all alphas to this file after learning (in the same order as in the training set) Structure learning options: --b float -> value of L2-bias feature. A value of 0 implies not having a bias feature. (default 1) WARNING: This is implemented only for linear kernel! --p [0..] -> fraction of positive examples to use as value of k for Prec@k and Rec@k. 0 indicates to use (0.5 * #pos) for Prec@k and (2 * #pos) for Rec@k. #pos is the number of positive examples in the training set. (default 0) --t [0..] -> Use sparse kernel expansion. Values like those for normal kernel (i.e. option -t). (default 0) --k [0..] -> Specifies the number of basis functions to use for sparse kernel approximation. (default 500) --f string -> Specifies file that contains basis functions to use for sparse kernel approximation. (default training file) The following loss functions can be selected with the -l option: 0 Zero/one loss: 1 if vector of predictions contains error, 0 otherwise. 1 F1: 100 minus the F1-score in percent. 2 Errorrate: Percentage of errors in prediction vector. 3 Prec/Rec Breakeven: 100 minus PRBEP in percent. 4 Prec@k: 100 minus precision at k in percent. 5 Rec@k: 100 minus recall at k in percent. 10 ROCArea: Percentage of swapped pos/neg pairs (i.e. 100 - ROCArea).
SVMperf learns an unbiased linear classification rule (i.e. a rule sign(w*x) without explicit threshold). Using the parameter '--b', an artificial feature with constant value is added to each training example which acts like a threshold. The loss function to be optimized is selected using the '-l' option. Note that I never really tested Prec@k and Rec@k, so take those with a grain of salt.
You can in principle use kernels in SVMperf using the '-t' option just like in SVMlight, but it is painfully slow. Much faster (but only approximate) is using a sparse kernel expansion via the option '--t' (to be described in a future paper). The number of basis functions to use is specified with '--k'. The more basis functions, the more accurate the approximation but the longer the training time. Normally, the basis functions are sampled from the training set, but you can give a file with an explicit set of basis function using the '--f' option. The file has the same format as a training/test file.
The file format of the training and test files is the same as for SVMlight. The first lines may contain comments and are ignored if they start with #. Each of the following lines represents one training example and is of the following format:
The target value and each of the feature/value pairs are separated by a space character. Feature/value pairs MUST be ordered by increasing feature number. Features with value zero can be skipped. The target value denotes the class of the example via a positive integer. So, for example, the line
-1 1:0.43 3:0.12 9284:0.2 # abcdef
specifies an negative example (i.e. -1) for which feature number 1 has the value 0.43, feature number 3 has the value 0.12, feature number 9284 has the value 0.2, and all the other features have value 0. In addition, the string abcdef is stored with the vector, which can serve as a way of providing additional information when adding user defined kernels.
The result of svm_perf_learn is the model which is learned from the training data in train.dat. The model is written to model.dat. To make predictions on test examples, svm_perf_classify reads this file. svm_perf_classify is called as follows:
svm_perf_classify [options] test.dat model.dat predictions
For all test examples in test.dat the predicted classes are written to the file predictions. There is one line per test example in predictions in the same order as in test.dat.
You will find an example problem at
Download this file into your svm_perf directory and unpack it with
gunzip -c example1.tar.gz | tar xvf -
This will create a subdirectory example1. There are 2000 examples in the file train.dat and 600 in the file test.dat. To run the example, execute the commands:
svm_perf_learn -c 20 -l 2 --b 0 example1/train.dat example1/model
svm_perf_classify example1/test.dat example1/model example1/predictions
The accuracy on the test set is printed to stdout. The equivalent call to SVMlight that will find the same classification rule (up to numerical precision) is svm_learn -c 1 -b 0 example1/train.dat example1/model.
This software is free only for non-commercial use. It must not be distributed without prior permission of the author. The author is not responsible for implications from the use of this software.