**Problem :**

I am facing following error message:

**Index in position 1 is invalid. Array indices must be positive integers or logical values.**

My code is as follows:

clc;

close all;

clear;

PD=phantom('Modified Shepp-Logan');

padimage = [2,2];

PD= padarray(PD,padimage);

subplot(2,3,1)

imagesc(PD);

colormap('gray');

title('Circle Phantom')

xlabel('X')

ylabel('Y')

freq = 2;

thetas = 0:freq:180;

gtheta = length(thetas);

gl = size(PD,1);

sinogram = zeros(gl,gtheta);

for i = 1:length(thetas)

tmpImage = imrotate(PD,-thetas(i),'bilinear','crop');

sinogram(:,i) = sum(tmpImage);

end

subplot(2,3,2)

imagesc(sinogram);

title('Circle Sinogram');

xlabel('l');

ylabel('\theta');

thetas=0;

Fl = size(sinogram,1);

Ftheta = length(thetas);

thetas = (pi/180)*thetas;

g0 = zeros(Fl,Fl);

Fmid = ceil(Fl/2);

[x,y] = meshgrid(ceil(-Fl/2):ceil(Fl/2-1));

for i = 1:Ftheta

rotCoords = Fmid+round(x*sin(thetas(i)) + y*cos(thetas(i)));

rotCoords=floor(abs(rotCoords));

g0 = g0 + sinogram(rotCoords,i)./Ftheta;

end

subplot(2,3,3);

imagesc(g0);

title('Simple backprojection')

xlabel('X')

ylabel('Y')

The error message is occurring as follow:

**Index in position 1 is invalid. Array indices must be positive integers or logical values.**

Can anybody tell me why the issue is here?