How to find the position of points in a coordinate system?

I am new to MatLab and still learning how to use 'for' loops correctly, as I may not even need to use one here.

I am trying to set up a coordinate system which will then cycle through every point and find the distance. I have coded the coordinate system like so:

x_step = 0.01;
z_step = 0.02;
Z = (-5:z_step:5);
X = (0:x_step:5);

which leaves me with two vectors, both with dimensions of 1-by-501.

Now the equation I am using to calculate the response at some point in the coordinate space is:

How would I write code which tells me the distance at each point?

I have had a go at writing a simple for loop which just outputs one value which I assume is the last. Here is the code:

for i = X
    for j = Z 
        R = sqrt(i.^2+j.^2);
    end
end

Please, any tips/advice or help would be greatly appreciated! Thanks.

Answer 1

[Alex Mcaulley]

Using for loops:

R = zeros(numel(X),numel(Z));
for i = X
    for j = Z 
        R(i,j) = sqrt(i.^2+j.^2);
    end
end

[Daniel Tanner]

Hi, thanks for replying so quickly!

So I have tried it this way and result in the error:

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

Error in Untitled4 (line 11)
        R(i,j) = sqrt(i.^2+j.^2);

Which I am not sure what that means.

[Alex Mcaulley]

Then, the solution should be:

x_step = 0.01;
z_step = 0.02;
Z = (-5:z_step:5);
X = (0:x_step:5);

R = zeros(numel(X),numel(Z));
for i = 1:numel(X)
    for j = 1:numel(Z) 
        R(i,j) = sqrt(X(i).^2+Z(j).^2);
    end
end

Or a better solution:

x_step = 0.01;
z_step = 0.02;
Z = (-5:z_step:5);
X = (0:x_step:5);

[Z,X] = meshgrid(Z,X);
R = sqrt(X.^2+Z.^2);

And still better

x_step = 0.01;
z_step = 0.02;
Z = (-5:z_step:5);
X = (0:x_step:5);
R = sqrt(Z.^2+X'.^2);