Out of memory Recursive call problem

Hello everyone.

I am trying to make a famous Split and merge algorithm on MATLAB for line extraction.

The error is Out of memory. The likely cause is an infinite recursion within the program.

Error in task1>split (line 88)

[alpha1, r1, idx1] = split(x, y, start, splitPos+start-2, threshold);

I know this question has been asked earlier but Being a beginner in MATLAB, I do not understand how program is going to infinite recursion and how can I avoid it ?? Can anyone tell me the mistake ?? The code is given below.

clc;
close all;
clear all;

threshold = 50;

M = csvread('data.csv');
[m, n] = size(M);
lst = int64(n/6);
for i = 1: lst
    index = 6*i-4;
    rho(i) = M(1,index);
end
 
theta = zeros(1, lst);
max_angle = (7*pi)/6;
min_angle = -pi/6;
angle_diff = (max_angle - min_angle)/double(lst);

angle = max_angle;
for i = 1:16
    theta(1,i) = angle;
    angle = angle - angle_diff;
end
angle = min_angle;
for j = lst:-1:17
    theta(1,j) = angle;
    angle = angle + angle_diff;
end

%------------------------- Polar Coordiates Done----------------------

[x,y] = pol2cart(theta, rho);
x = -x;
plot(x,y,'o');
N = length(x);
[alpha, r, idx] = split(x,y,1, N,threshold);






function [alpha, r, idx] = split(x,y,start, ending, threshold)


N = ending - start + 1;
delX = x - (sum(x)/N);
delY = y - (sum(y)/N);
num   = -2 * sum(delX.*delY);
denom = sum(delY.*delY - delX.*delX);

alpha = atan2(num, denom) / 2;
% compute parameter r by inserting the controid into the line equation and solve for r
r = ((sum(x)/N) * cos(alpha)) + ((sum(y)/N) * sin(alpha));

%-----------------------Line fit done---------------------------------

cosA = cos(alpha);
sinA = sin(alpha);
  
N = size(x,2);
d = zeros(N,1);
  
xcosA = x * cosA;
ysinA = y * sinA;
d = xcosA + ysinA - r;

%-------------------------- Distance calculated ----------------------

    farOnPositiveSideB = d > threshold;
    farOnNegativeSideB = d < -threshold;
    
    neigborsFarAwayOnTheSameSideI = find((farOnPositiveSideB(1:N-1) & farOnPositiveSideB(2:N)) | (farOnNegativeSideB(1:N-1) & farOnNegativeSideB(2:N)));
   
    if isempty(neigborsFarAwayOnTheSameSideI) 
        splitPos = -1;
    else
        absDPairSum = abs(d(neigborsFarAwayOnTheSameSideI)) + abs(d(neigborsFarAwayOnTheSameSideI+1));
        [ans, splitPos] = max(absDPairSum);
        splitPos = neigborsFarAwayOnTheSameSideI(splitPos);
        if abs(d(splitPos)) <= abs(d(splitPos + 1)), splitPos = splitPos + 1; end
    end

% ------------------------ Split Position calculated --------------------
    
    if (splitPos ~= -1) % found a splitting point
        [alpha1, r1, idx1] = split(x, y, start, splitPos+start-2, threshold);
        [alpha2, r2, idx2] = split(x, y, splitPos+start-1, ending, threshold);
        alpha = [alpha1; alpha2];
        r = [r1; r2];
        idx = [idx1; idx2];
    else % no need to split
        idx = [start, ending];
    end 
    return
end

Answer 1

[Image Analyst]

In your split routine, at this line

[alpha1, r1, idx1] = split(x, y, start, splitPos+start-2, threshold);

you cal split() again. So it goes deeper in. And then it geta called again so it goes even deeper. And deeper and deeper forever until it runs out of memory. Your exit strategy before that line, where you set splitPos to -1 (so it will back itself out) evidently never happens, so it just keeps going deeper.

You should set a breakpoint in the routine to try to figure out why splitPos never gets assigned to -1.

[hafizas101]

Yes. Thank you very much. When I increased threshold to very large, splitPos became -1 and further working on code also made me realize few other mistakes. thanks.