필터 지우기
필터 지우기

How to manually calculate the score values for Gaussian SVM?

조회 수: 6 (최근 30일)
Yanran
Yanran 2023년 2월 18일
답변: Vanshika Vaishnav 2023년 3월 7일
I have trained an SVM using the following hyperparameters:
where data_pt are NP by 2 training data points and data_val contains a column vector of 1 or 0. I am trying to construct a score function to calculate the prediction score for a new observation. As it mentioned in the documentation, "you must first apply any transformations to the predictor data that were applied during training. Specifically, if you specify 'Standardize',true when using fitcsvm, then you must standardize the predictor data manually by using the mean SVMModel.Mu and standard deviation SVMModel.Sigma, and then divide the result by the kernel scale in SVMModel.KernelParameters.Scale", I belive I did that. However, the output value I get are just the basis for any input prediction X. Does anyone have any idea what I did wrong? Thank you so much!
Here is my code:
function [s,dsdx,dsdy] = myscore_gaussian(x,Mdl)
% output:
% s: the manual calculation of prediction score for the predictor data x
% (scalar)
% inputs:
% 1. x: (1 by 2 vector) the x and y coordinates of the predictor data,
% must within the trained x and y limits
% 2. Mdl: the trained SVM model
% s(x) = sum(from i = 1 to NS) alpha_i y_i K(x_i,x) + b
% Get parameters for the trained Mdl
kscale = Mdl.KernelParameters.Scale;
alpha = Mdl.Alpha;
bias = Mdl.Bias;
sv = Mdl.SupportVectors;
[NS,~] = size(sv);
mu = Mdl.Mu;
sigma = Mdl.Sigma;
svclass = Mdl.SupportVectorLabels;
% standarize the input predictor x
xd = (x - mu)./sigma/kscale;
s = 0;
dsdx = 0;
dsdy = 0;
for i = 1:NS
svi = sv(i,:);
alphai = alpha(i);
yi = svclass(i);
temp = -((svi(1)-xd(1))^2 + (svi(2)-xd(2))^2);
ki = exp(temp);
tempdx = 2*(svi(1)-xd(1));
tempdy = 2*(svi(2)-xd(2));
s = s + alphai*yi*ki;
dsdx = dsdx + alphai*yi*ki*tempdx;
dsdy = dsdy + alphai*yi*ki*tempdy;
end
s = s + bias;

답변 (1개)

Vanshika Vaishnav
Vanshika Vaishnav 2023년 3월 7일
If SVMModel.KernelParameters.Function is 'linear', then the classification score for the observation x is
f(x)=(x/s)β+b.
SVMModel stores β, b, and s in the properties Beta, Bias, and KernelParameters.Scale, respectively.
For more information, refer the below documentation:-

제품


릴리스

R2022b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by