I've used the gmdistribution to fit data to a Gaussian mixture model. I wanted to plot a contour plot http://imgur.com/yVE1M where the contours are obviously missing. For a 1D problem I found fplot, but now I'm stumped.
I ran into a similar problem when I wrote an EM algorithm for gaussian mixtures. Here is the snippet of code that fixed it in my case:
for l=1:k
zz=gmdistribution(MU(l,:),SIG(:,:,l),PI(l));
ezcontour(#(x,y)pdf(zz,[x y]),[minx1 maxx1],[miny1 maxy1],250);
end
The key is to increase N:
ezcontour(...,N) plots FUN over the default domain using an N-by-N
grid. The default value for N is 60.
Related
I'm having troubles when fitting a pdf to an histogram in Matlab. I'm using gmdistribution.fit because my data is multi-modal. This is what I have done:
data=[0.35*randn(1,100000), 0.5*randn(1,100000)+5, 1*randn(1,100000)+3]'; %multimodal data
x=min(data):(max(data)-min(data))/10000:max(data);
%Normalized Histogram
[counts,edges]=histcounts(data,500, 'Normalization', 'pdf');
bw=edges(2)-edges(1);
centers=edges(1:end-1)+bw;
H = bar(centers,counts,'hist');
hold on
%Fitting with gmdistribution
rng default
obj=gmdistribution.fit(data,3,'Replicates',5);
%the PDF
PDF=zeros(1,length(x));
for i=1:obj.NumComponents
k=obj.ComponentProportion(i);
u=obj.mu(i);
sigma=obj.Sigma(i);
PDF=PDF+k*normpdf(x,u,sigma);
end
PDF=PDF/trapz(x,PDF); %normalization (just in case)
plot(x,PDF)
%Fitting with ksdensity (for comparison)
[PDF2,xi]=ksdensity(data,x);
plot(x,PDF2)
legend('Normalized Histogram','gmdistribution','ksdensity')
Histogram and PDFs
As you can see, the Gaussian Mixture doesn't fit the histogram properly. The PDF from the ksdensiti function is much better. I have also tried to fit just one gaussian. If you run the same previous code, using
data=[0.35*randn(1,100000)]';
and
obj=gmdistribution.fit(data,1,'Replicates',5);
you get the following
Histogram and PDFs for one gaussian
Again, the pdf from gmdistribution doesn't fit the histogram. It seems that the problem is with the scaling factor in the data generation (the 0.35). What am I doing wrong?
The Sigma parameter of the gmdistribution object corresponds to the covariance, however, the normpdf function needs the standard deviation. The problem is fixed by replacing normpdf(x,u,sigma) with normpdf(x,u,sqrt(sigma)) in the for loop.
So... I am working on part b and I haven no idea what this question is asking me to do. Does it want me to plot the actual Q(x) equation graph with part a graphs?
It appears as if you need to plot the pdf(x) and cdf(x) and compare to the estimated pdf and cdf you obtained for the different values of t.
I have a 100 x 100 matrix and i have to use plot3 in MATLAB environment to graph this data. I tried plot3(matrix name) but I faced this error "not enough input arguments". I think plot3 needs 3 input arguments, but I only have this matrix of data. could anyone help me to solve this problem? Is there any alternative for plot3 when we don't have enough arguments?
I need a graph like this:
I think you want to plot the values in a figure as a sort of surface element. What you can do then is:
[X,Y] = size(matrix);
figure;
surface(1:X,1:Y,matrix);
What this does is that it creates a vector for both X and Y indices, as possible in surface. The X and Y indices are obtained by setting them as integers from 1:size, so basically you assign the location of each matrix element to an index.
Note that you can strictly speaking use surface(matrix) as well, but the former approach allows you to use custom indexing, as long as the lengths of the vectors X and Y are the same as the size of your matrix.
For the waterfall use:
figure;
waterfall(matrix);
Sample code:
A=rand(100);
figure;
waterfall(1:100,1:100,A);
Gives:
where you can play around with the name-value pairs, see the documentation on that.
I think what you need is mesh or surf instead of plot3.
plot3 draws a line in 3d-space, so it will need three vectors of the same length (one for each dimension).
When you have a matrix, one reasonable way of displaying it is as a surface in 3d space, which is done by the functions mesh and surf.
Try it out! I hope i helps!
How to plot a 3D figure in MATLAB based on a function like f(x,y,z)=0?
And this complicated function can not be written as z = f(x,y).
f(x,y,z)=sum(a.*exp(sv(:,1)-x).^2+sv(:,2)-y).^2+sv(:,3)-z).^2)-b=0
where a is a known vector, sv is a known matrix, b is a known value. x,y,z are three variables. How to draw this surface in 3D way in matlab?
I just solve this question by this tool from the Matlab File Exchange:
Ezimplot3: implicit 3D functions plotter
your function only contains 1D vectors( I am assuming they are of equal lengths), if summed it will give you a constant; therefore, there is really nothing to plot.
I'm pretty new to Matlab and I would like to make a plot with errorbars. I have the errors in a vector expressed in % of the measured values. I have tried to use Matlab's errorbar but it is only shifting the plot in a strange way.
Standard usage is errorbar(x,y,yerr, ...options...).
In your case sounds like yerr = y.*percenterr/100