Where is the mistake? This code doesn't work.

clc;
close all;
clear all;
syms x;
% Four Arm Mechanism

%global LAB LBC LDC LEF LEC LAD LAG LGD LAF
LAB=0.09;%m
LBC=0.4;%m
LDC=0.12;%m
LEF=0.21;%m
LEC=0.25;%m
LAD=0.22;%m
LAG=0.35;%m
LGD=0.22;%m
LAF=0.4;%m 
Nmax = 100; % max number of iterations
epsk = [1e-6, 1e-6]; % convergence threshold
tet2o = 135 * pi / 180

tet2o = 2.3562

tet3o = 20 * pi / 180; % rad, initial value of theta3
tet4o = 320 * pi / 180; % rad, initial value of theta4
eps = [0, 0]; % error vector
% Pre-allocate arrays
th2 = 0:1:360; N=length(th2);
teta2 = zeros(1, N); % theta2 in radians
teta3 = zeros(1, N); % theta3 in radians
teta4 = zeros(1, N); % theta4 in radians
teta5 = zeros(1, N);
tet3 = zeros(1, N); % theta3 in degrees
tet4 = zeros(1, N); % theta4 in degrees

%% wbar = waitbar(0, 'Iteration Processing....'); % progress bar
k = 0; % iteration counter
% Loop through values of theta2
for tet2 = 0:1:360
    k = k + 1;
    tet2 = pi * tet2 / 180; % Convert to radians
    teta2(k) = tet2;
    tet1o = pi *60 / 180; % Convert to radians
    tet3o = 20 * pi / 180; % Reset initial value of tet3o
    tet4o = 320 * pi / 180; % Reset initial value of tet4o
    tet5o = 30 * pi / 180;
    % Loop through iterations
    for iter = 1:Nmax
        % Update theta3 and theta4
        tet3o = tet3o + eps(1);
        tet4o = tet4o + eps(2);
        % Define function and Jacobian
        f = [(LDC * sin(teta3(k)) + LEF * sin(tet5o) -LEC * sin(teta4(k))); (LDC * cos(teta3(k)) + LEF * cos(tet5o) -LEC * cos(tet4o))];
        J = [-LEF * cos(tet5o), -LEC * cos(tet4o);-LEF * sin(tet5o), LEC * sin(tet4o)];
        % Compute error and check for convergence
        eps = inv(J)*f;
        if abs(eps(1)) <= epsk(1) && abs(eps(2)) <= epsk(2)
            kiter = iter; % number of iterations to converge
            tet3(k) = tet3o * 180 / pi; % deg
            teta1(k) = tet1o
            teta3(k) = tet3o; % rad
            teta4(k) = tet4o; % rad
            tet4(k) = teta4(k) * 180 / pi; % deg
            break;
        end
    end
end
%% close(wbar);
fid = fopen('reportfourarm.m', 'w');
fprintf(fid, 'teta2(i) teta3(i) teta4(i)\n');
for i = 1:N
    fprintf(fid, '%1.2f     %6.1f        %6.1f\n', i-1, tet3(i), tet4(i));
end
fclose(fid);
%% kon=input(' Analysis Results: Report | <enter>\n');
%% if kon==0
%% end
t=0:1:N-1;
tet4 = 0:1:360;
tet5 = 0:1:360;
360;
% Plot the trajectory of theta_3 and theta_4
plot(t, tet4, 'r-', t, tet4, 'b-', t, tet3, 'g-');
xlabel('Theta (rad)');
ylabel('Theta (deg)');
legend('Theta_3', 'Theta_4', 'Theta_5');
title('Trajectory of Theta_4, Theta_5,');

[Dyuman Joshi]

I have commented out the code which does not work on the live editor here (with double percentage symbols) and ran the code, and the code runs without an error (see above).

What is supposed to be the "mistake"?

How are you running the code? As a script/function? Live script?

Does any error occurs when you run the code? If so, please share the full error message (i.e. all of the red text) and mention does it error occur in the parts I commented out?

[Furkan]

I want to find a graph with theta3 in the x plane and theta4 and theta5 in the y plane, how can I find it?

[Furkan]

also thank you

Answer 1

[Dev]

Hi Furkan,

In order to plot data onto specific planes in MATLAB R2023b, I am assuming that by “plot on specific planes” you aim to change the coordinate positions of ‘Theta_3’ from ‘X’ to ‘Y’. To do the same, we can leverage the following variant of the plot function-

plot(X1, Y1, LineSpec1, .., Xn, Yn, LineSpecn);

More information on this specific plot function variant can be referred to at the below link (mentioned as the 4th variant)-

https://www.mathworks.com/help/releases/R2024a/matlab/ref/plot.html

Assuming that the code shared above is ran in R2023b, the correct plot function is used but the ‘X’ and ‘Y’ axis values would require a correction. Please refer to the modified plot function call mentioned below (the graph title has been modified accordingly and executed in R2023b)-

% Plot the trajectory of theta_4 and theta_5 against theta_3
plot(t, tet4, 'r-', t, tet5, 'b-', tet3, t, 'g-');
xlabel('Theta (rad)');
ylabel('Theta (deg)');
legend('Theta_3', 'Theta_4', 'Theta_5');
title('Trajectory of Theta_4 and Theta_5 vs Theta_3');

After executing the modified plot function, we can see the correct graph plotted in figure below-

Here, ‘Theta_3’ is now plotted against ‘X’, but the legend is not visible since the code computes ‘Theta_3’ as all zeros. Also,‘Theta_5’ is now against ‘Y’ (green axis), which was earlier along ‘X’.

Hope it addresses the issue.

[Dyuman Joshi]

I am not sure why you have mentioned that particular syntax of plot() as something novel when OP is already using it.

"After executing the modified plot function, we can see the correct graph plotted in figure below-"

How do you know that that is the correct graph? Your assumption could be wrong.

And the order of legend in your answer does not match the order of plots and there's a mis-match in your comment and what your code does.

"Here, ‘Theta_3’ is now plotted against ‘X’, but the legend is not visible since the code computes ‘Theta_3’ as all zeros. "

This is wrong -

1. The line is not visible.The legend is.

2. If the legend was not visible, the values being all zeroes wouldn't have anything to do with that -

x = 10*rand(1,5);
y = zeros(1,5);
plot(x, y, 'r-')
legend('Random Numbers (0,10)')

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