Why is nothing showing up on my plots?

Question

Jade Cruz 2023-7-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1992143-why-is-nothing-showing-up-on-my-plots

回答： Star Strider 2023-7-5

All three plots won't show the iterations from my calculation.

% Simulate the system

for k = 1:(tf - t0)/dt

% Update the reference joint positions

q_r = q + dt*qdr;

% Calculate the Jacobian

J = calc_jacobian(q, L1, L2, L3);

% Update the actual joint positions

q = q_r + dt*J'*qdr;

% Plot the results

if k == 1

plot_results(q, J);

end

function plot_results(q, J)

% Plot the joint positions

subplot(3, 1, 1)

hold on

plot(q(1), 'b')

plot(q(2), 'r')

plot(q(3), 'g')

xlabel('Time (s)')

ylabel('Joint angle (deg)')

% Plot the Jacobian determinant

subplot(3, 1, 2)

plot(J'*J)

xlabel('Time (s)')

ylabel('Jacobian determinant')

% Plot the end-effector pose

subplot(3, 1, 3)

plot(q(1), q(2), 'b*')

xlabel('x (m)')

ylabel('y (m)')

axis([-2, 4, -2, 4])

end

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Sandeep Mishra 2023-7-5

I have answered that for example case with 3 different figures.

If you still face any error, do comment

Jade Cruz 2023-7-5

@Sandeep Mishra Thank you for your help! I have posted a comment below your answer. I appreciate the continuous support.

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Answer 1

Steven Lord 2023-7-5

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在 MATLAB Online 中打开

When you call plot with just a color in the line specification, what you get is a plot with no markers.

h = plot(1, 'b');

h.Marker

ans = 'none'

What does a line "connecting" one point look like? Nothing. If instead you'd specified a marker in addition to a color, you'd get a line "connecting" one point and a marker on that point.

figure

h = plot(1, 'bx');

If you want to create a plot where you add points to a line iteratively, I'd use the animatedline function to create the line then call addpoints on the animated line. You won't be able to see the iterative process in Answers, but if you run the code below in an interactive session of MATLAB you'll see the plot appear, point by point.

x = 0:360;

y = sind(x);

figure

axis([0 360 -1 1])

h = animatedline('LineStyle', '-', 'Color', 'b');

for k = 1:numel(x)

addpoints(h, x(k), y(k))

pause(1/32)

end

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Jade Cruz 2023-7-5

Thank you so much. This was what I was thinking. I will try this out!

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Answer 2

Sandeep Mishra 2023-7-5

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https://ww2.mathworks.cn/matlabcentral/answers/1992143-why-is-nothing-showing-up-on-my-plots#answer_1267743

编辑：Torsten 2023-7-5

在 MATLAB Online 中打开

Hello Jade,

I understood from our discussion in the comments that you are trying to plot multiple plots (in your case = 50)

In MATLAB, you can use figure(n) to create a figure with number property is equal to n.

You can refer the below example code (plot with 3 figures)

clear;

% Define the parameters

L1 = 4;

L2 = 3;

L3 = 2;

dt = 0.1;

t0 = 0;

tf = 5;

q0 = [10, 20, 30]';

qdr = [0.2, -0.3, -0.2]';

% Initialize the variables

q = q0;

J = zeros(3, 3);

% for k = 1:(tf - t0)/dt

% Example

for k = 1:3

% Update the reference joint positions

q_r = q + dt*qdr;

% Calculate the Jacobian

J = calc_jacobian(q, L1, L2, L3)

% Update the actual joint positions

q = q_r + dt*J'*qdr

% Plot the results

figure(k)

plot_results(q, J);

end

J = 3×1

5.7498 -4.7984 1.0000

q = 3×1

10.2589 20.2089 30.2189

J = 3×1

7.0790 -2.0237 1.0000

q = 3×1

10.4612 20.3612 30.3812

J = 3×1

7.1168 0.3353 1.0000

q = 3×1

10.5935 20.4435 30.4735

function J = calc_jacobian(q,L1,L2,L3)

% Calculate the Jacobian

J = [-L1*sin(q(1)) - L2*sin(q(1) + q(2)) - L3*sin(q(1) + q(2) + q(3));

L1*cos(q(1)) + L2*cos(q(1) + q(2)) + L3*cos(q(1) + q(2) + q(3));

1];

end

function plot_results(q, J)

% Plot the joint positions

subplot(3, 1, 1)

hold on

plot(q(1), 'b')

plot(q(2), 'r')

plot(q(3), 'g')

xlabel('Time (s)')

ylabel('Joint angle (deg)')

% Plot the Jacobian determinant

subplot(3, 1, 2)

plot(J'*J)

xlabel('Time (s)')

ylabel('Jacobian determinant')

% Plot the end-effector pose

subplot(3, 1, 3)

plot(q(1), q(2), 'b*')

xlabel('x (m)')

ylabel('y (m)')

axis([-2, 4, -2, 4])

end

You can refer to the below documentation to learn more about "figure" in MATLAB.

https://in.mathworks.com/help/matlab/ref/figure.html#d124e460113

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Jade Cruz 2023-7-5

编辑：Jade Cruz 2023-7-5

That is perfect but I do notice that all the figures do not show any sort of information or plot. Would the problem be my equations and not my code?

Sandeep Mishra 2023-7-5

I hope @Steven Lord cleared your doubt @Jade Cruz ?

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Answer 3

Star Strider 2023-7-5

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1992143-why-is-nothing-showing-up-on-my-plots#answer_1267778

在 MATLAB Online 中打开

It now fills the matrices corrrectly and plots something, however I cannot determine what you want it to plot —

% Regarding the missing values:

% Define the parameters

L1 = 4;

L2 = 3;

L3 = 2;

dt = 0.1;

t0 = 0;

tf = 5;

q0 = [10, 20, 30]';

qdr = [0.2, -0.3, -0.2]';

% Initialize the variables

q(:,1) = q0;

J = zeros(3, 3);

kv = 1:(tf - t0)/dt; % Create Vector

for k = 1:numel(kv)

% Update the reference joint positions

q_r(:,k+1) = q(:,k) + dt*qdr; % Subscript Result (Create Matrix Of Column Vectors)

% Calculate the Jacobian

J(:,k+1) = calc_jacobian(q(:,k), L1, L2, L3); % Subscript Result (Create Matrix Of Column Vectors)

% Update the actual joint positions

q(:,k+1) = q_r(:,k) + dt*J(:,k)'*qdr; % Subscript Result (Create Matrix Of Column Vectors)

end

% Plot the results

figure

plot(q, J)

grid

xlabel('q')

ylabel('J')

title('Original Matrices')

figure

plot(q.', J.')

grid

xlabel('q')

ylabel('J')

title('Transposed Matrices')

function J = calc_jacobian(q,L1,L2,L3)

% Calculate the Jacobian

J = [-L1*sin(q(1)) - L2*sin(q(1) + q(2)) - L3*sin(q(1) + q(2) + q(3));

L1*cos(q(1)) + L2*cos(q(1) + q(2)) + L3*cos(q(1) + q(2) + q(3));

1];

end

I defer to you to figure out how to plot the results.

.

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