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问题 I have a bivariate gaussian I defined as follow: I=[1 0;0 1];
mu=[0,0];
sigma=0.5*I;
beta = mvnrnd(mu,sigma,100); %100x2 matrix where each column vector is a variable.
now I want to plot a contour of the pdf of the above matrix. What I did: Z = mvnpdf(beta,mu,sigma); %100x1 pdf matrix
Now I want to plot a contour of the bivariate gaussian beta. I know I should
use the command contour but this one require Z to be a square matrix. how do I
solve this? I am very confused and not sure how to plot the contour of the
bivariate gaussian!! ANY HELP IS GREATLY APPRECIATED..
Thank you 解答： You need to define your
x, y axes and use meshgrid (or
ndgrid) to generate all combinations of x, y values, in the form of
two matrices X and Y. You then compute the
Z values (your Gaussian pdf) for those X and
Y, and plot Z as a function of X ,
Y using contour (contour plot), or perhaps
surf (3D plot). mu = [0,0]; %// data
sigma = [.5 0; 0 .5]; %// data
x = -5:.1:5; %// x axis
y = -4:.1:4; %// y axis
[X Y] = meshgrid(x,y); %// all combinations of x, y
Z = mvnpdf([X(:) Y(:)],mu,sigma); %// compute Gaussian pdf
Z = reshape(Z,size(X)); %// put into same size as X, Y
%// contour(X,Y,Z), axis equal %// contour plot; set same scale for x and y...
surf(X,Y,Z) %// ... or 3D plot
 转自：http:///questions/20170083/plot-a-contour-of-multivariate-normal-pdf-of-a-given-mvn-in-matlab
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