Questions tagged [libsvm]

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58 views

Implementing a weighted support vector machine in python

I have the following problem. The minimization problem of the SVM that I want to solve is: $$ \min_{w, b} \frac{1}{2}w^{T}w + \sum^{m}_{i=1}C_{i}xi_{i} $$ Subject to: $$ y_{i}(w^{T}x_{i} - b) \geq 1 - ...
2
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1answer
772 views

Convert Pandas Dataframe with mixed datatypes to LibSVM format

I have a pandas data frame with about Million rows and 3 columns. The columns are of 3 different datatypes. NumberOfFollowers is of a numerical datatype, UserName is of a categorical data type, ...
0
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1answer
47 views

SVM SVC: Metric for parameter optimization on imbalanced data

I trained a multiclass SVC with RBF kernel on a down-sampled (and therefore balanced) dataset. Now I want to perform grid search to find best cost and gamma. What performance metric should I optimize ...
1
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0answers
24 views

Practical examples/tutorials of using One-Class Support Vector Machines

I am a newbie in machine learning, and hope to solve an anomaly detection task using One-Class Support Vector Machines (OCSVM). ...
0
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1answer
703 views

Linear SVM in matlab and python giving different results

I have a particular dataset on which I am getting different results when using a linear SVM in matlab and sklearn toolbox. The data has been normalized in matlab and imported into python from a mat ...
2
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1answer
1k views

Why Liblinear performs drastically better than libsvm linear kernel?

l have a dataset of dim=(200,2000) 200 examples and 2000 features. l have 10 classes. l used sklearn for both cases : svm.svc(kernel=linear) LinearSVC() ...
4
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1answer
4k views

What is the difference between Linear SVM and SVM with linear kernel?

I'm wondering whether there is a difference between Linear SVM and SVM with a linear kernel. Or is a linear SVM just a SVM with a linear kernel? If so, what is the difference between the two ...
-2
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1answer
2k views

Where can I find python code for SVM that use multiple feature data? [closed]

I am trying do an Image Classification where each sample of training data contains data of the current pixel with the 8 surrounding ones. Where can I find examples of SVM, in python, that use 5 or ...
1
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0answers
59 views

Obtain standard deviation for libsvm

I have the following code for Grid search, but it only return the accuracy result using 5 folds cross-validation. Is it possible to obtain standard deviation from the 5 folds CV. How would you do that?...
0
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2answers
3k views

Is standardization needed before using scikit-learn SVM?

I am using the SVM function provided by scikit-learn. I would like to know whether I need to perform standardization before fitting the model. As I know, LibSVM ...
1
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0answers
89 views

$\chi^{2}$ kernel SVM performance issue

I am using $\chi^{2}$ kernel for non-linear SVM (using libSVM) for classifying MNIST digits. I am getting very bad performance (worse than random guessing). The $\chi^{2}$ kernel code (in MATLAB) is ...
1
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2answers
200 views

Prepare data for SVM, Is it valid to normalise the data before and after PCA dimension reduction

Is it valid to normalise a dataset, reduce dimensionality with PCA and then to normalise the reduced dimension data. Assuming this is performed on training data, should the same PCA coefficients be ...
0
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2answers
543 views

Understanding text conversion into SVM input [closed]

In Support Vector Machines, when used for sentiment analysis, text gets converted into a set of data points. How does this happen, usually?
17
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2answers
411 views

Use liblinear on big data for semantic analysis

I use Libsvm to train data and predict classification on semantic analysis problem. But it has a performance issue on large-scale data, because semantic analysis concerns n-dimension problem. Last ...