MatLab自带的SVM一共集成了两个函数： svmtrain和 svmclassify。 1.首先查看你的MatLab版本是否已经集成了SVM，我的版本R2013a，主要参考MatLab帮助文档(自带demo) >> help svmtrain svmtrain Train a support vector machine classifier SVMSTRUCT = svmtrain(TRAINING, Y) trains a support vector machine (SVM) classifier on data taken from two groups. TRAINING is a numeric matrix of predictor data. Rows of TRAINING correspond to observations; columns correspond to features. Y is a column vector that contains the known class labels for TRAINING. Y is a grouping variable, i.e., it can be a categorical, numeric, or logical vector; a cell vector of strings; or a character matrix with each row representing a class label (see help for groupingvariable). Each element of Y specifies the group the corresponding row of TRAINING belongs to. TRAINING and Y must have the same number of rows. SVMSTRUCT contains information about the trained classifier, including the support vectors, that is used by SVMCLASSIFY for classification. svmtrain treats NaNs, empty strings or 'undefined' values as missing values and ignores the corresponding rows in TRAINING and Y.
2.下面是使用文档： SVMSTRUCT = svmtrain(TRAINING, Y, 'PARAM1',val1, 'PARAM2',val2, ...) specifies one or more of the following name/value pairs: Name Value 'kernel_function' A string or a function handle specifying the kernel function used to represent the dot product in a new space. The value can be one of the following: 'linear' - Linear kernel or dot product (default). In this case, svmtrain finds the optimal separating plane in the original space. 'quadratic' - Quadratic kernel 'polynomial' - Polynomial kernel with default order 3. To specify another order, use the 'polyorder' argument. 'rbf' - Gaussian Radial Basis Function with default scaling factor 1. To specify another scaling factor, use the 'rbf_sigma' argument. 'mlp' - Multilayer Perceptron kernel (MLP) with default weight 1 and default bias -1. To specify another weight or bias, use the 'mlp_params' argument. function - A kernel function specified using @(for example @KFUN), or an anonymous function. A kernel function must be of the form function K = KFUN(U, V) The returned value, K, is a matrix of size M-by-N, where M and N are the number of rows in U and V respectively. 'rbf_sigma' A positive number specifying the scaling factor in the Gaussian radial basis function kernel. Default is 1. 'polyorder' A positive integer specifying the order of the polynomial kernel. Default is 3. 'mlp_params' A vector [P1 P2] specifying the parameters of MLP kernel. The MLP kernel takes the form: K = tanh(P1*U*V' + P2), where P1 > 0 and P2 < 0. Default is [1,-1]. 'method' A string specifying the method used to find the separating hyperplane. Choices are: 'SMO' - Sequential Minimal Optimization (SMO) method (default). It implements the L1 soft-margin SVM classifier. 'QP' - Quadratic programming (requires an Optimization Toolbox license). It implements the L2 soft-margin SVM classifier. Method 'QP' doesn't scale well for TRAINING with large number of observations. 'LS' - Least-squares method. It implements the L2 soft-margin SVM classifier. 'options' Options structure created using either STATSET or OPTIMSET. * When you set 'method' to 'SMO' (default), create the options structure using STATSET. Applicable options: 'Display' Level of display output. Choices are 'off' (the default), 'iter', and 'final'. Value 'iter' reports every 500 iterations. 'MaxIter' A positive integer specifying the maximum number of iterations allowed. Default is 15000 for method 'SMO'. * When you set method to 'QP', create the options structure using OPTIMSET. For details of applicable options choices, see QUADPROG options. SVM uses a convex quadratic program, so you can choose the 'interior-point-convex' algorithm in QUADPROG. 'tolkkt' A positive scalar that specifies the tolerance with which the Karush-Kuhn-Tucker (KKT) conditions are checked for method 'SMO'. Default is 1.0000e-003. 'kktviolationlevel' A scalar specifying the fraction of observations that are allowed to violate the KKT conditions for method 'SMO'. Setting this value to be positive helps the algorithm to converge faster if it is fluctuating near a good solution. Default is 0. 'kernelcachelimit' A positive scalar S specifying the size of the kernel matrix cache for method 'SMO'. The algorithm keeps a matrix with up to S * S double-precision numbers in memory. Default is 5000. When the number of points in TRAINING exceeds S, the SMO method slows down. It's recommended to set S as large as your system permits. 'boxconstraint' The box constraint C for the soft margin. C can be a positive numeric scalar or a vector of positive numbers with the number of elements equal to the number of rows in TRAINING. Default is 1. * If C is a scalar, it is automatically rescaled by N/(2*N1) for the observations of group one, and by N/(2*N2) for the observations of group two, where N1 is the number of observations in group one, N2 is the number of observations in group two. The rescaling is done to take into account unbalanced groups, i.e., when N1 and N2 are different. * If C is a vector, then each element of C specifies the box constraint for the corresponding observation. 'autoscale' A logical value specifying whether or not to shift and scale the data points before training. When the value is true, the columns of TRAINING are shifted and scaled to have zero mean unit variance. Default is true. 'showplot' A logical value specifying whether or not to show a plot. When the value is true, svmtrain creates a plot of the grouped data and the separating line for the classifier, when using data with 2 features (columns). Default is false. SVMSTRUCT is a structure having the following properties: SupportVectors Matrix of data points with each row corresponding to a support vector. Note: when 'autoscale' is false, this field contains original support vectors in TRAINING. When 'autoscale' is true, this field contains shifted and scaled vectors from TRAINING. Alpha Vector of Lagrange multipliers for the support vectors. The sign is positive for support vectors belonging to the first group and negative for support vectors belonging to the second group. Bias Intercept of the hyperplane that separates the two groups. Note: when 'autoscale' is false, this field corresponds to the original data points in TRAINING. When 'autoscale' is true, this field corresponds to shifted and scaled data points. KernelFunction The function handle of kernel function used. KernelFunctionArgs Cell array containing the additional arguments for the kernel function. GroupNames A column vector that contains the known class labels for TRAINING. Y is a grouping variable (see help for groupingvariable). SupportVectorIndices A column vector indicating the indices of support vectors. ScaleData This field contains information about auto-scale. When 'autoscale' is false, it is empty. When 'autoscale' is set to true, it is a structure containing two fields: shift - A row vector containing the negative of the mean across all observations in TRAINING. scaleFactor - A row vector whose value is 1./STD(TRAINING). FigureHandles A vector of figure handles created by svmtrain when 'showplot' argument is TRUE. Example: % Load the data and select features for classification load fisheriris X = [meas(:,1), meas(:,2)]; % Extract the Setosa class Y = nominal(ismember(species,'setosa')); % Randomly partitions observations into a training set and a test % set using stratified holdout P = cvpartition(Y,'Holdout',0.20); % Use a linear support vector machine classifier svmStruct = svmtrain(X(P.training,:),Y(P.training),'showplot',true); C = svmclassify(svmStruct,X(P.test,:),'showplot',true); errRate = sum(Y(P.test)~= C)/P.TestSize %mis-classification rate conMat = confusionmat(Y(P.test),C) % the confusion matrix See also svmclassify, NaiveBayes, classregtree, classify, TreeBagger, groupingvariable
Reference page in Help browser doc svmtrain 文档最佳观看效果：在MatLab中使用doc svmtrain命令
3.一个例子：Examples Find a line separating the Fisher iris data on versicolor and virginica species, according to the petal length and petal width measurements. These two species are in rows 51 and higher of the data set, and the petal length and width are the third and fourth columns.
load fisheriris xdata = meas(51:end,3:4); group = species(51:end); svmStruct = svmtrain(xdata,group,'showplot',true);
另外，这个写的不错(例子写的非常好)： 《(Matlab)SVM工具箱快速入手简易教程》 ps.关于例子，百度文库里有结果图可看，其他各种转载的博客上无图。
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