Trouble with using the function 'solve' to obtain decision boundary

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nazneen 2015-2-3

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https://ww2.mathworks.cn/matlabcentral/answers/174924-trouble-with-using-the-function-solve-to-obtain-decision-boundary

评论： Star Strider 2015-2-20

I need to find the point where the decision boundary occurs for a single feature of the iris data set. I am certain i need to solve the equation P(x/SWL) = P(x/VWL) and obtain the solutions for x.I get an error for the code i tried below. The error states x is an undefined variable. Can you tell me where i am going wrong?

load fisheriris
SWL=meas(1:50,1)
VWL=meas(51:100,1)
V1 = var(SWL);
V2 = var(VWL);
M1 = mean(SWL);
M2 = mean(VWL);
P1 = (1/(sqrt(2*pi*V1))*(exp(((x-M1)^2)/(2*V1))));
P2 = (1/(sqrt(2*pi*V2))*(exp(((x-M2)^2)/(2*V2))));
solve(P1-P2);

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采纳的回答

Star Strider 2015-2-3

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https://ww2.mathworks.cn/matlabcentral/answers/174924-trouble-with-using-the-function-solve-to-obtain-decision-boundary#answer_166836

在 MATLAB Online 中打开

The easiest way is to use the fzero function:

P1 = @(x) (1/(sqrt(2*pi*V1))*(exp(((x-M1)^2)/(2*V1))));     % ‘P1’ As Anonymous Function
P2 = @(x) (1/(sqrt(2*pi*V2))*(exp(((x-M2)^2)/(2*V2))));     % ‘P2’ As Anonymous Function
X = fzero(@(x) P1(x)-P2(x), 1)                              % Create Anonymous Funciton, Solve For ‘x’

produces: