issue in defining struct input

Question

How to define a structure input called mixture with the following fields: mu1, sigma1, mu1, sigma2, and wts in the following Matlab function:

   function plotMixtureGaussians( mixture )

        % determine the contour described by the mixture
        m1 = mixture.mu1';
        s1 = mixture.sigma1;
        m2 = mixture.mu2';
        s2 = mixture.sigma2;
        w1 = mixture.wts(1);
        w2 = mixture.wts(2);

       xlim = -5:0.1:5;
       ylim = -5:0.1:5;
       [x,y] = meshgrid( xlim, ylim );

        z = zeros( length(xlim), length(ylim) );
        for ii = 1:length(xlim)
            for jj = 1:length(ylim)
                X = [x(ii,jj), y(ii,jj)]';
                t1 = w1 * gaussian2D( X, m1, s1 );
                t2 = w2 * gaussian2D( X, m2, s2 );
                if t1 > t2
                z(ii,jj) = 1;
                else 
                z(ii,jj) = -1;
               end
           end
        end

        contour(x,y,z, 'XData', xlim, 'YData', ylim)
        hold on;

        % plot the means
        x = [ mixture.mu1(1) mixture.mu2(1)];
        y = [ mixture.mu1(2) mixture.mu2(2)];
        plot( x, y, 'r.', 'Markersize', 5);

        % plot the individual gaussians
        plotGaussian( m1, s1, xlim, ylim );
        plotGaussian( m2, s2, xlim, ylim );
        end

       function p = gaussian2D( X, mu, s )
       p = (1/( 2 *pi *det(s)^2) * exp(-0.5 * (X - mu)' * (s \ (X-mu)) ));
   end

    function plotGaussian( mu, s, xlim, ylim )

        hold on
        [x,y] = meshgrid( xlim, ylim );

        z = zeros( length(xlim), length(ylim) );
        for ii = 1:length(xlim)
            for jj = 1:length(ylim)
                X = [x(ii,jj), y(ii,jj)]';
                z(ii,jj) = gaussian2D( X, mu, s ); 
            end
        end
        contour(x,y,z, 'XData', xlim, 'YData', ylim);
    end

How to define struct input called mixture with the specified fields to get the above script work. — user3001418
– user3001418, Commented Oct 28, 2015 at 16:25

Adriaan · Accepted Answer · 2015-10-28 16:34:07Z

1

I would first reference you to the manual entry on Matlab structures. But, the simplest thing to do would be to define it as:

mixture.mu1 = 1;
mixture.sigma1 = 1;
mixture.mu2 = 1;
mixture.sigma2 = 1;
mixture.wts = [1 1];

Of course, you'd enter the values you wanted for the fields of the structure.

A shorter way of doing the above would be:

mixture = struct('mu1', 1, 'mu2', 1, 'sigma1', 1, 'sigma2', 1, 'wts', [1 1]);

edited Oct 28, 2015 at 16:34

Adriaan

18.2k7 gold badges47 silver badges88 bronze badges

answered Oct 28, 2015 at 16:30

houtanb

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