Storing output values from a for loop into an "array"

Hello everyone,

I am trying to output the values that I get from a for loop into an "array". I am not sure how to store those "list of values" into an array

I have attached my code in reference:

Storing_Values_Into_Array.m

close all; clc;

% Value of j
j = 1i;

% For the region k_o < k_p < sqrt(u_r*e_r)*k_o
% Wavenumber in free space value = k_o
k = 2*pi;
% Permeability Value = u_r
u_r = 1;
% Permittivity Value e_r
e_r = 2.2;
% Value of kz_1
kz_1 = @(kp) sqrt((k).^2*e_r*u_r - (kp).^2);
% Value of kz_2
kz_2 = @(kp) sqrt((kp).^2 - (k).^2);
% Substrate heights = d
D = [0.02 0.04 0.06 0.08 0.10];

% Using a for loop to calculate the roots for T_M 
% Solving for k_p values
for i=1:numel(D)
d=D(i);
% Equations for TM(kp)
T_M = @(kp) kz_1(kp).*sin(d.*kz_1(kp)) - e_r*kz_2(kp).*cos(d.*kz_1(kp));
kp_root=[fzero(T_M, [k , k*sqrt(e_r*u_r)])]
fplot(T_M,[k k*sqrt(e_r*u_r)], 'LineWidth',3); hold on
plot(kp_root,0,'o','MarkerSize',8,'MarkerFaceColor','k');
ylim([-5 5]);
xlim([k k*sqrt(e_r*u_r)]);
title('T_M vs k_p')
ylabel('T_M')
xlabel('k_p')
grid on;
ax = gca;
ax.GridLineWidth = 2;
end; hold off



%{
What I am trying to do is store the values I get from "kp_root" in an
array called "kp_list" so I can use that array for calculations later on.
%}

Answer 1

[Ayush Modi]

Hi Ammar,

I am assuming you want to append the kp_root values you obtain in each iteration of for loop and store them in the variable kp_list. You can achieve it by concatenation.

Here is code snippet for your reference -

% Initialize an empty array kp_list before the for loop
kp_list = []

% After you get the value of kp_root in for loop, concatenate kp_root to kp_list
kp_root=[fzero(T_M, [k , k*sqrt(e_r*u_r)])]
kp_list = [kp_list kp_root]

For more information refer to the following MathWorks documentation:

• Concatenation - https://www.mathworks.com/help/matlab/math/creating-and-concatenating-matrices.html
• Matrices and Arrays - https://www.mathworks.com/help/matlab/matrices-and-arrays.html

[Ammar]

Thank you @Ayush Modi for the quick response. This worked!

Answer 2

[Vandit]

Hello Ammar,

To store the values from "kp_root" in an array called "kp_list", you can initialize an empty array before the for loop and then append each value of "kp_root" to the array inside the loop. Here's the updated code with the "disp" command at the end to display the values stored in the "kp_list" array:

close all; clc;

% Value of j
j = 1i;

% For the region k_o < k_p < sqrt(u_r*e_r)*k_o
% Wavenumber in free space value = k_o
k = 2*pi;

% Permeability Value = u_r
u_r = 1;

% Permittivity Value e_r
e_r = 2.2;

% Value of kz_1
kz_1 = @(kp) sqrt((k).^2*e_r*u_r - (kp).^2);

% Value of kz_2
kz_2 = @(kp) sqrt((kp).^2 - (k).^2);

% Substrate heights = d
D = [0.02 0.04 0.06 0.08 0.10];

% Initialize kp_list array
kp_list = [];

% Using a for loop to calculate the roots for T_M 
% Solving for k_p values
for i = 1:numel(D)
    d = D(i);

    % Equations for TM(kp)
    T_M = @(kp) kz_1(kp).*sin(d.*kz_1(kp)) - e_r*kz_2(kp).*cos(d.*kz_1(kp));

    kp_root = fzero(T_M, [k , k*sqrt(e_r*u_r)]);

    kp_list = [kp_list, kp_root]; % Append kp_root to kp_list

    fplot(T_M, [k k*sqrt(e_r*u_r)], 'LineWidth', 3); hold on
    plot(kp_root, 0, 'o', 'MarkerSize', 8, 'MarkerFaceColor', 'k');
    ylim([-5 5]);
    xlim([k k*sqrt(e_r*u_r)]);
    title('T_M vs k_p')
    ylabel('T_M')
    xlabel('k_p')
    grid on;
    ax = gca;
    ax.GridLineWidth = 2;
end
hold off

disp(kp_list);

In the above code snippet, an empty array "kp_list" is initialized before the loop, and the roots found in each iteration(kp_root) are appended to "kp_list" inside the loop so that "kp_list" will contain all the roots after the loop.

To know more about Matrices and Arrays in MATLAB, you can refer to the following documentation:

https://www.mathworks.com/help/matlab/matrices-and-arrays.html

Hope this helps.