Changing variable in a looped code

Hi, I have been trying to figure this out for a while. It will help in many cases.

I have a set of variables as such;

x1 = [3 4 5 2 3];

x2 = [4 2 7 8 3];

x3 = [8 2 9 3 9];

y = [1 5 3 8 5];

I would like to write a looped program in which the x variable in use would change in each loop. for example,

for i=1:3
  plot(x,y)

    hold all

end

I would like the program to use x1 for the first loop and than x2 for the second loop and so on.

I have tried writing xi but that does not work.

Thanks,

Answer 1

[Ilham Hardy]

hint:

doc eval

[Thomas]

You have to be very careful while using eval http://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

http://blogs.mathworks.com/loren/2005/12/28/evading-eval/

[Ilham Hardy]

For this particular use (plotting), IMHO, i do not see the danger of utilizing eval. However i would like to be corrected.

for id = 1:3
eval(['plot(x' num2str(id) ',y)'])
hold all
end

[Mazhar]

Just read up the document about eval.

How exactly will I add this to my code above?

[Ilham Hardy]

Just refresh your browser :P

[Mazhar]

Ah! Cheers :D

[Mazhar]

Ok I see how it works with the plot command. But now I'm trying to include it in to other calculations, for example

z = [4 1 3 4 5];

for k=1:3
  distance = z - x;

    distancesqr = distance' * distance;

end

again the for the first loop x1 is used and then x2 for the second loop and so on.

[Ilham Hardy]

Then it is (for many reasons that will be described by another fellow member :D) discouraged using the eval.

If you have a possibility (and will) to change/adjust the x. Then it will better to transform x into cell array.

e.g.

x1 = [3 4 5 2 3];
x2 = [4 2 7 8 3];
x3 = [8 2 9 3 9];

x_all = {x1;x2;x3};

y = [1 5 3 8 5];
z = [4 1 3 4 5];

% pre-allocate
distancesqr=cell(1,3);

for id = 1:3
%eval(['plot(x' num2str(id) ',y)'])
figure(1)
plot(x_all{id},y)
hold all

distance = z - x_all{id};
distancesqr{id} = distance' * distance;

end

%bonus
figure(2)
plot(distancesqr{:},y)

Answer 2

[rifat]

for i=1:3
string=['plot(x' num2str(i) ',y);'];
eval(string);
end

I think this will do

Answer 3

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F