Date: Feb 20, 2013 12:24 PM
Author: Jerome
Subject: Subscript indices must either be real positive integers or logicals Error + Code

was wondering if someone can explain to me what this error means. And, if possible, how to resolve it? ??? Subscript indices must either be real positive integers or logicals.

Error in ==> interp2>linear at 344
F = ( arg3(ndx).*(onemt) + arg3(ndx+1).*t ).*(1-s) + ...

Error in ==> interp2 at 220
zi = linear(ExtrapVal,x,y,z,xi,yi);

Error in ==> snake at 71
ssx = gamma*xs - kappa*interp2(fx,xs,ys);

This is my complete code:

image = imread('image.jpg');

%parameters
alpha = 0.001;
beta = 0.4;
kappa=0.0001;
gamma = 100;
N = 100;
wl = 10;
we = 10;
wt = 10;
smth = rgb2gray(image);

% Calculating size of image
[row col] = size(image)

eline = smth; %eline is simply the image intensities

[grady,gradx] = gradient(double(smth));

eedge = -1 * sqrt ((gradx .* gradx + grady .* grady)); %eedge is measured by gradient in the image

m1 = [-1 1];
m2 = [-1;1];
m3 = [1 -2 1];
m4 = [1;-2;1];
m5 = [1 -1;-1 1];

cx = conv2(smth,m1,'same');
cy = conv2(smth,m2,'same');
cxx = conv2(smth,m3,'same');
cyy = conv2(smth,m4,'same');
cxy = conv2(smth,m5,'same');

for i = 1:700
for j= 1:900
% eterm as deined in Kass et al Snakes paper
eterm(i,j) = (cyy(i,j)*cx(i,j)*cx(i,j) -2 *cxy(i,j)*cx(i,j)*cy(i,j) + cxx(i,j)*cy(i,j)*cy(i,j))/((1+cx(i,j)*cx(i,j) + cy(i,j)*cy(i,j))^1.5);
end
end

eext = (double(wl.*eline) + double(we.*eedge -wt) .* eterm); %eext as a weighted sum of eline, eedge and eterm

[fx, fy] = gradient(eext); %computing the gradient

xs=1:900;
xs=xs';
ys=repmat(242,1,900);
ys=ys'

[m n] = size(xs);
[mm nn] = size(fx);

%populating the penta diagonal matrix
A = zeros(m,m);
b = [(2*alpha + 6 *beta) -(alpha + 4*beta) beta];
brow = zeros(1,m);
brow(1,1:3) = brow(1,1:3) + b;
brow(1,m-1:m) = brow(1,m-1:m) + [beta -(alpha + 4*beta)]; % populating a template row
for i=1:m
A(i,:) = brow;
brow = circshift(brow',1)'; % Template row being rotated to egenrate different rows in pentadiagonal matrix
end

[L U] = lu(A + gamma .* eye(m,m));
Ainv = inv(U) * inv(L); % Computing Ainv using LU factorization

%moving the snake in each iteration
for i=1:N;

ssx = gamma * xs - kappa * interp2(fx,xs,ys); %This is where I receive the error
ssy = gamma * ys - kappa * interp2(fy,xs,ys);

%calculating the new position of snake
xs = Ainv * ssx;
ys = Ainv * ssy;


%Displaying the snake in its new position
% imshow(image,[]);
% hold on;
plot([xs; xs(1)], [ys; ys(1)], 'r-');
% hold off;
% pause(0.001)
end;