My function is stuck in a loop

I'm writing an function to detect corners in certain images, it runs forever. If I pause after 2 minutes, it ends up in the function INDEX listed at the bottom ([edit Rik: the give_index function was bold]). BAsed on my playing around with the ebugging tool, it never leaves the INDEX function. The value of INDEX is always zero. I'm not sure why, can anyone deliver some insight?

I apologize for the code dump, please ask any questions if you need clarification.

clc
clear
close all
IMAGE_1 = imread('Building1.jpg');
IMAGE_2 = imread('CheckerBoard.jpg');


SIGMA = 1;
X = -2:1:2; % Setting up gaussian filter
H = [];

for i = 1 : 5
    
    H(i) = exp(-X(i)^2/(2*SIGMA^2))/(SIGMA * sqrt(2*3.14));
end

H = H / min(H);
H = H / sum(H); 
I_s = uint8(conv2(H,H', IMAGE_1));
[row,col] = size(I_s);


grad = [-1 0 1];    % Setting up gradient
E_x = conv2(I_s,grad);
E_x = imresize(E_x,[row, col]);
E_y= conv2(I_s,grad');
E_y = imresize(E_y, [row,col]);
INPUT = 'Input N \n';
N = input(INPUT);
INPUT = 'Type desired Tau \n';
TAU = input(INPUT);
L = [];

for i = 2:row-1
    for j = 2 : col -1 
        C = [E_x(i,j)^2,E_x(i,j)*E_y(i,j);E_x(i,j)*E_y(i,j),E_y(i,j)^2];
        TEMP = eig(C);
        if TEMP(2) > TAU
            L(end+1,:) = [TEMP(2),[i,j]];
        end
    end
end

L = sortrows(L,1,'descend');
[row_L, col_L] = size(L);

for i = 1 : row_L
    % Check N
    TEMP = L(i,:);
    row_temp = TEMP(2);
    col_temp = TEMP(3);
    % Determine appropiate matrix
    if row_temp-N>1 && row_temp+N<row && col_temp-N>1 && col_temp+N<col
        for m = row_temp-N : row_temp+N
            for n = col_temp-N : col_temp+N
                if m ~= row_temp && n ~= col_temp
                   L_row_ind = find(L(:,2) == m);
                   L_col_ind = find(L(:,3) == n);
                   INDEX = give_index(L_row_ind,L_col_ind);
                   if INDEX ~= 0 
                       L(INDEX,:) = 0;
                   end
                end
            end
        end
    end
end
%% delete rows contain 0 i.e. garma2 = 0
L = L(any(L,2),:);
plot(L(:,2),L(:,3),'x')

function INDEX = give_index(x,y)
INDEX = 0;

for i = 1 : size(x)
    for j = 1 : size(y)
        if x(i) == y(j)
            INDEX = x(i);
            return
        end
    end
end
end

Answer 1

[Rik]

That give_index function looks like it is very slow and may return unexpected results for non-integer inputs. It will also only operate along the first dimension, because size returns a vector. You should consider creating such loops with numel instead of size.

clear
%generate random integers to avoid floating point rounding errors
x=randi(10,100,1);
y=randi(10,100,1);
isequal(give_index(x,y),give_index2(x,y))

%suggested function
function INDEX = give_index2(x,y)
L=ismembertol(x,y,2*eps,'DataScale',1);
if any(L)
    INDEX=x(find(L,1));
else
    INDEX = 0;
end
end

%your function for reference
function INDEX = give_index(x,y)
INDEX = 0;
for i = 1 : size(x) % should be replaced by numel(x)
    for j = 1 : size(y) % should be replaced by numel(y)
        if x(i) == y(j) % should be replaced by abs(x(i)-y(i))<=2*eps
            INDEX = x(i);
            return
        end
    end
end
end

Answer 2

[Image Analyst]

You say

if x(i) == y(j)

Are x and y floating point numbers? If so, see the FAQ: https://matlab.fandom.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

You should use ismembertol().