Tagged Questions

1
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2answers
39 views

How to interpret the model parameters of libsvm via MATLAB interface?

I used the MATLAB interface of libsvm for doing binary classification of 997-dimensional training data. I am trying to understand how the resulting model is used to compute the predicted output (which ...
2
votes
2answers
67 views

Why can the margin of SVM be approximated by 1?

The separate function of SVM is : $wx+b=0$ The function distance of support vector to the separate plane is : $|r| = wx_i+b$ And we can normalize the $w$, then the distance can be write as : ...
0
votes
1answer
49 views

regularized logistic regression and support vector machine

L2 regularized logistic regression differs with L2 regularized support vector machine with their loss function. Are there more deep differences for these two models? I tried several data sets, and ...
0
votes
1answer
59 views

The Lagrange multipliers of SVM

Actually the solve the SVM is to solve the following Lagrangian Equation: If we don't use kernel function, $\langle x^{(i)},x^{(j)}\rangle$ is just the vector vector inner product. The ...
1
vote
1answer
25 views

Bias term in support vector machine

In SVM, there is a bias term. But looks to me there are very few discussions on the physical meanings of this term. Why should we have that? How does this term affect the model?
1
vote
3answers
61 views

Order of Support Vectors, and how to reduce them

I am working in an extremely memory constrained environment, and the number of support vectors my Matlab design is generating is just not something that scales. That led me to move to finding a way to ...
1
vote
0answers
23 views

Weighted SVM and Up-sampling

I'm performing classification with the libSVM package in R and am wondering about the correct procedure for weighting or up-sampling. I have a data set that is 19,396 observations of which only 81 are ...
0
votes
2answers
48 views

In SVM, what are the labels and how do you get them from the data?

I'm working on a school project and have decided to use SVM for stock market prediction. I have a 1000x5 matrix of stock quotes containg data for open, close, high, low, volume data. From what I ...
0
votes
0answers
25 views

coordinated dual descent method and sequential minimal optimization

Libsvm uses the sequential minimal optimization as its main solver while Liblinear uses coordinated dual descent method. What are the major differences between these two methods? Looks like both of ...
0
votes
1answer
126 views

understanding of libsvm output

I applied libsvm to build a text classifier. The output looks like as follows: ...
2
votes
1answer
125 views

Using the appropriate machine learning algorithm

I am not sure if this is the right forum to ask this. I have some data of the houses, like their size(in square meters), if they use aircondition, how many residents live in, I have their electricity ...
0
votes
1answer
55 views

liblinear one vs rest learn parameters

Liblinear (http://www.csie.ntu.edu.tw/~cjlin/liblinear/) does not support for probability estimates. Say I have three classes C1, C2 and C3. I want to learn the model paramters for each 'one vs rest' ...
0
votes
0answers
56 views

LIBSVM-based classifier assign very low score to positive validation files

Recently, I have been applying the LIBSVM to build a classifier based on a set of documents. The positive set has about 20000 files and negative set has about 50000 files. The built classifier is then ...
0
votes
2answers
232 views

Which SVM kernel to use for a binary classification problem?

I'm a beginner when it comes to support vector machines. Are there some guidelines that say which kernel (e.g. linear, polynomial) is best suited for a specific problem? In my case, I have to classify ...
0
votes
0answers
53 views

the effects of feature matrix format on the training time of LIBSVM

I am using Libsvm to perform text classification tasks. I normally uses binary occurrence, TF/IDF to build feature set for the input documents. It normally takes quite longer for Libsvm to finish ...
2
votes
0answers
144 views

Bias items and probability estimates in LibSVM

I have two questions in using LIBSVM The decision function for C-support vector classification is $$\text{sgn}\left(w^T\phi(x)+b\right)=\text{sgn}\left(\sum_{i=1}^ly_i\alpha_iK(x_i,x)+b\right)$$ ...
0
votes
0answers
98 views

SVM with svm and svmpath function

I am trying to compare the R functions svm (library: e1071) and svmpath (library svmpath). ...
1
vote
2answers
574 views

LibSVM cost weights for unbalanced data doesn't work

I have a data set that number of negative labeled values are 163 times of number of positive labeled values so I have a unbalanced data set. I have tried that: ...
3
votes
1answer
910 views

How to use libSVM for one-class SVM problems?

I plan to use libSVM for a one-class svm problem, but I'm not sure about the meaning of nu in svm_parameter. Does it mean the ...
0
votes
1answer
343 views

libSVM for unbalanced data

I'm using libSVM for binary classification and my training data is very unbalanced (-1:90%, +1:10%). According to libSVM's documentation, it's better to set different penalties for positive and ...
1
vote
1answer
234 views

probablistic output for binary SVM classification

I'm using libSVM for a binary classification problem. After a test instance is assigned a label (1 or -1), I also want to know how likely it is assigned such a label. I'm thinking about calculating ...
0
votes
1answer
56 views

a question on multiplicative SMV kernel

I'm new to SVM and would like to use it to solve a problem formulated, for example, as follows: The patterns are four-dimensional vectors $(x_1,x_2,x_3,x_4)$, and the kernel is $K(\bf{x_i}, ...
1
vote
1answer
108 views

The general approaches for improving a SVM-based classifier which is low precision and high recall

I built a SVM-based classifier against a data set, the precision is about 66% and the recall is about 88%. Generally, what are the options to tune the parameter that can increase the precision?
1
vote
1answer
168 views

Different prediction score for two SVM-based classifiers

As a validation study, I use two libsvm-based svm classifier against the same data set. One classifier is libsvm implementation in Rapidminer. Another classifier is Libsvm itself. Both of them assume ...
3
votes
2answers
167 views

Use of the Gamma parameter with support vector machines

When using libsvm, the parameter $\gamma$ is a parameter for the kernel function. Its default value is setup as $\frac{1}{Number Of Features}$ Is there any ...
2
votes
1answer
720 views

libsvm “reaching max number of iterations” warning and cross-validation

I'm using libsvm in C-SVC mode with a polynomial kernel of degree 2 and I'm required to train multiple SVMs. Each training set has 10 features and 5000 vectors. During training, I am getting this ...
2
votes
1answer
211 views

Calculate probability for LibLinear classification results

I am using LibLinear for a document classification task, in which I would like to calculate the probability of correctness for each prediction. In fact, in the LibLinear, it does provide probability ...
5
votes
3answers
425 views

Support vector machine for text classification

I am currently having a data set, class 1 with about 8000 short text files and class 2 with about 3000 short text files. I applied LibSVM and tried a couple of parameter combinations in the ...
1
vote
2answers
287 views

rb-libsvm - getting confidence of a prediction

I'm using rb-libsvm and the RBF kernel to make classifications. svm.predict(measurements) returns either -1.0 or 1.0. Is there a way to get a confidence for this ...
4
votes
2answers
430 views

Cross validation and prediction for unknown data

How do we build a model, cross validate it and use it to predict for unknown data? Say I have a known dataset of 100 points. Steps for 10 fold cross-validation are- Divide the data randomly into ...
8
votes
2answers
1k views

What is the influence of C in SVMs with linear kernel?

I'm currently using an SVM with a linear kernel to classify my data. There is no error on the training set. I tried several values for the parameter C (10^-5, ..., 10^2). This did not change the error ...
6
votes
3answers
458 views

Is it possible to append training data to existing SVM models?

I'm using libsvm and I noticed that everytime I call svmtrain(), I create a new model and that there seems to be no option to put data in an existing model. Is this possible to do however? Am I just ...
1
vote
0answers
308 views

One class classification with LIBSVM in Weka

I have a dataset on a particular domain and I want to do a one-class classification with LIBSVM (wrapper) in Weka. I have trained the classifier, but the problem is, when I test it with a different ...
1
vote
1answer
376 views

Support Vector Machines (SVM) maximum margin hyperplane use

I have been approaching to Support Vector Machines in this period, and I need a clarification about the use of the maximum margin hyperplane. From a labeled point training set, we train a model that ...
3
votes
1answer
168 views

Can an svmlight model be converted to work with libsvm?

I have a model file that was created using svmlight in classification mode with a linear kernel. Is it possible to convert this file so that libsvm can use it for classifying?
9
votes
2answers
702 views

Problem with e1071 libsvm?

I have a dataset with two overlapping classes, seven points in each class, points are in two-dimensional space. In R, and I'm running svm from e1071 package to build separating hyperplane for these ...
2
votes
2answers
511 views

Grid search and tolerance in libsvm

I'm using libsvm and the 3-fold cross validation to select the best C and gamma, but I'm not sure for the range to use in the grid search. Is there any standard way to choose this range? I used: ...