Why are my plots empty?

Question

Caitlynn Sengchiam 2022-2-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1658080-why-are-my-plots-empty

回答： ag 2024-1-4

clear;clc;
%Known Values
r2=140; %input
r3=70.1; %known
r4=70.1; %known
rBE=47.1; %known
r5=140; %unknown
rBC=47.1; %known
theta2=0; %known
theta3=60; %unknown
theta4=60; %unknown
os4=10; %offset from theta4
thetaBE=theta4+os4;%known
theta5=0; %unknown
os3=10; %offset from theta3
thetaBC=theta3+os3; %known
e = zeros(4,360);
%Position
while r2 <= 360
    error = 1;
    x = [theta3;theta4;theta5;r5]; %Matrix of Initial Guesses
    tol = 1e-8;
    i = 0;
   
    while ((error > tol) && (i < 1000))
       
        f = fun(x,r2);
        j = jac(x);
        deltax = j\f;
        xnew = x - deltax;
        error = abs ((xnew - x)) ./ xnew;
        error = max(error);
        x = xnew;
        i = i + 1;
       
    end
       
   
    figure(1)
    p=plot(r2,x(1),'r.');
    xlabel('r2')
    ylabel('1')
    hold on
   
    figure(2)
    p=plot(r2,x(2),'b.');
    hold on
   
    figure(3)
    p=plot(r2,x(3),'g.');
    hold on
   
    figure(4)
    p=plot(r2,x(4),'c.');
    hold on
   
    e(:,r2) = x;
end
function [F] = fun(x,r2)
r3=70.1; %known
r4=70.1; %known
rBE=47.1; %known
rBC=47.1; %known
theta2=0; %known
thetaBE=70; %known
thetaBC=70; %known
F= [r2*cosd(theta2)+r3*cosd(x(1))-r4*cosd(x(2)); % for x: R2 + R3 - R4
    r2*sind(theta2)+r3*sind(x(1))-r4*sind(x(2)); % for y: R2 + R3 - R4
    rBE*cosd(thetaBE)-x(4)*cosd(x(3))-rBC*cosd(thetaBC); % for x: RBE - R5 - RBC
    rBE*sind(thetaBE)-x(4)*sind(x(3))-rBC*sind(thetaBC); % for y: RBE - R5 - RBC
    ];
end
function [J] = jac(x)
r3=70.1;
r4=70.1;
os3=10;
os4=10;
rBC=47.1;
rBE=47.1;
J=zeros(4,4);
J(1,1)=r3*cosd(x(1));
J(2,1)=-r3*sind(x(1));
J(3,1)=-rBC*cosd(x(1)+os3);
J(4,1)=rBC*sind(x(1)+os3);
J(1,2)=-r4*cosd(x(2));
J(2,2)=r4*sind(x(2));
J(3,2)=rBE*cosd(x(2)+os4);
J(4,2)=-rBE*sind(x(2)+os4);
J(1,3)=0;
J(2,3)=0;
J(3,3)=-x(4)*cosd(x(3));
J(4,3)=x(4)*sind(x(3));
J(1,4)=0;
J(2,4)=0;
J(3,4)=-cosd(x(3));
J(4,4)=sind(x(3));
end

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Caitlynn Sengchiam 2022-2-25

在 MATLAB Online 中打开

I have changed the while loop to a for loop and plotted outside of the loop. My code runs faster, but my plot is still empty.

for r2 = 1:360;
    error = 1;
    x = [theta3;theta4;theta5;r5]; %Matrix of Initial Guesses
    tol = 1e-8;
    i = 0;
   
    while ((error > tol) && (i < 1000))
       
        f = fun(x,r2);
        j = jac(x);
        deltax = (1:length(x))';
        for i = 1:length(x)
            jj=j;
            jj(:,i)=f;
            deltax(i)=det(jj) / det(j);
            jj=j;
        end
        xnew = x-deltax;
        error = abs((xnew-x)./xnew);
        error=max(error);
        x=xnew;
        i=i+1;
    end
    e1(:,r2) = x;
end
   r2=(1:360);
   
   figure(1)
   plot(r2,e1(1,:),'r.');
   ('\r_2 [^{o}]');
   hold on
   
   plot(r2,e1(2,:),'b.');
   ('\r_2 [^{o}]');
   hold on
   
   plot(r2,e1(3,:),'c.');
   ('\r_2 [^{o}]');
   hold on
   
   plot(r2,e1(4,:),'g.');
   ('\r_2 [^{o}]');
   hold on
   
   xlabel('r2')
   ylabel('outputs')
   legend('theta3','theta4','theta5','r5')

Arif Hoq 2022-2-25

在 MATLAB Online 中打开

I think the problem is in your function fun and jac. whenever your dividing in (deltax(k)=jacfunc(k) / ffunc(k)) the its return an inf. I have found 2 output. but still it needs more development.

%Known Values
r2=140; %input
r3=70.1; %known
r4=70.1; %known
rBE=47.1; %known
r5=140; %unknown
rBC=47.1; %known
theta2=0; %known
theta3=60; %unknown
theta4=60; %unknown
os4=10; %offset from theta4
thetaBE=theta4+os4;%known
theta5=0; %unknown
os3=10; %offset from theta3
thetaBC=theta3+os3; %known
e = zeros(4,360);
error = 1;
x = [theta3;theta4;theta5;r5]; %Matrix of Initial Guesses
tol = 1e-8;
ffunc = fun(x,r2);
jacfunc = jac(x);
deltax = (1:length(x))';
%Position
for r2 = 1:360
    i = 0;
    while ((error > tol) && (i < 1000))    
        for k = 1:length(x)
            deltax(k)=jacfunc(k) / ffunc(k);
        end
        xnew = x-deltax;
        error = abs((xnew-x)./xnew);
        error=max(error);
        x=xnew;
        i=i+1;
    end
    e1(:,r2) = x;
end
  
   figure(1)
   plot(e1(1,:),'o');
   ('\r_2 [^{o}]');
   hold on
   
   plot(e1(2,:),'*');
   ('\r_2 [^{o}]');
   hold on
   
   plot(e1(3,:),'--');
   ('\r_2 [^{o}]');
   hold on
   
   plot(e1(4,:),'o');
   ('\r_2 [^{o}]');
   hold on
   
   xlabel('r2')
   ylabel('outputs')
   legend('theta3','theta4','theta5','r5')

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Answer 1

ag 2024-1-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1658080-why-are-my-plots-empty#answer_1382951

Hi Caitlynn,

I understand that you are trying to plot the obtained results, and are getting an empty plot.

Arif's suspicion seems to be correct; the issue stems from the calculated values of "jac(x)", which are detailed below.

As you can observe, the cancellation occurring in the first two columns leads to a determinant of zero. Consequently, when applying the formula "deltax(i) = det(jj) / det(j)", you end up with "NaN" since it involves division by zero. Such "NaN" values cannot be plotted.

Note - Jacobian with a zero determinant indicates that there is no net change at that specific point in terms of rate.

Hope this helps!

Best Regards,

Aryan Gupta

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