How to use num2str?

Dear all, I have this part of code:

R = [0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1] % vector, which data saves from the for loop

for i = 1:numel (R)

    j = R(i);
    [('x' -num2str(j)).^2+ '(y-0.5).^2<0.1^2','x','y','z'];
select_fcn = inline('(x-j).^2+(y-0.5).^2<0.1^2','x','y','z');
img_2.elem_data = 1 +* elem_select(img_2.fwd_model, select_fcn);
output(i)= Q;
end

I try to change variable j (for example j = 0.1).

But this line: [('x' -num2str(j)).^2+ '(y-0.5).^2<0.1^2','x','y','z'] ; report an error (Error using + Matrix dimensions must agree.).

Does anybody know what´s wrong?

Thank you for your answers.

Answer 1

[Azzi Abdelmalek]

      ['x-' num2str(j) '.^2+ (y-0.5).^2<0.1^2,'  'x,'  'y,'  'z'];