ezplot not working unless global variable is written - matlab

Question

I'm trying to plot the following function
% k-nn density estimation
% localSearcher is a handle class responsible for finding the k closest points to x
function z = k_nearest_neighbor(x, localSearcher)
% Total point count
n = localSearcher.getPointCount();
% Get the indexes of the k closest points to x
% (the k parameter is contained inside the localSearcher class)
idx = localSearcher.search(x);
% k is constant
k = length(idx);
% Compute the volume (i.e. the hypersphere centered in x that encloses every
% sample in idx)
V = localSearcher.computeVolume(x, idx);
% The estimate for the density function is p(x) = k / (n * V)
z = k / (n * V);
end
I know for sure that the above algorithm is correct, because I get a reasonable plot using the following function
% Plot the values of k_nearest_neighbor(x, searcher) by sampling it manually
function manualPlot(samples, searcher)
a = -2;
b = 2;
n = 1000;
h = (b - a) / n;
sp = linspace(a, b, n);
pt = zeros(n);
areas = zeros(n);
estimated_pdf = #(x)k_nearest_neighbor(x, searcher);
area = 0;
for i = 1 : length(sp)
x = sp(i);
pt(i) = estimated_pdf(x);
area = area + h * pt(i);
areas(i) = area;
end
figure, hold on
title('k-nn density estimation');
plot(sp, pt, sp, areas, ':r');
legend({'$p_n(x)$', '$\int_{-2}^{x} p_n(x)\, \, dx$'}, 'Interpreter', 'latex', 'FontSize', 14);
plot(samples,zeros(length(samples)),'ro','markerfacecolor', [1, 0, 0]);
axis auto
end
called by
function test2()
clear all
close all
% Pattern Classification (page 175)
samples = [71 / 800; 128 / 800; 223 / 800; 444 / 800; 475 / 800; 546 / 800; 641 / 800; 780 / 800];
% 3-nn density estimation
searcher = NaiveNearestSearcher(samples, 3);
manualPlot(samples, searcher);
end
which outputs
However, if I try to do the same thing with ezplot
% Plot the values of k_nearest_neighbor using ezplot
function autoPlot(samples, searcher)
estimated_pdf = #(x)k_nearest_neighbor(x, searcher);
figure, hold on
ezplot(estimated_pdf, [-2,2]);
title('k-nn density estimation');
legend({'$p_n(x)$', '$\int_{-2}^{x} p_n(x)\, \, dx$'}, 'Interpreter', 'latex', 'FontSize', 14);
plot(samples,zeros(length(samples)),'ro','markerfacecolor',[1,0,0]);
axis auto
end
I get the following incorrect result
No warnings are issued from the console.
It's like the searcher parameter passed to the anonymous function
estimated_pdf = #(x)k_nearest_neighbor(x, searcher);
ezplot(estimated_pdf, [-2,2]);
goes "out of scope" (or something) before ezplot terminates.
The really weird thing is that adding
function z = k_nearest_neighbor(x, localSearcher)
[... same identical code ... ]
global becauseWhyNotVector;
% becauseWhyNotVector(end + 1) = 1; NOT WORKING, I must use the x variable for some reason
becauseWhyNotVector(end + 1) = x;
end
apparently fixes the problem (!).
Here's the full source code, I'm using MATLAB R2011a.