What is the error? 1, fast

clc;
clear;
close;
global th_3 th_5  R L4 L5 L3 th_2  
R=5;
L3=19;
L4=44;
L5=31;
n=1; %num of rev
m=360*n; % num of dev of theta

acc=1;
a=1/acc;

th_r=linspace(0,2*pi ,m)
double th_2 
%syms th_3 th_5 th_r
eg1= ((asin((L3*sind(th_3)-R*sind(th_r))/L5)) - th_5) ;
eg2= ((acos(-(R*cosd(th_r)+L5*cosd(th_5)-L4)/L3)) -th_3)  ;
th_2 =( th_3-110)
th_r = th_r +a;

figure(1)
plot(th_2 , th_r)
grid on;

Message:

ans =

116 104 95 50

th_2 =

th_3 - 110

Error using plot

Data must be numeric, datetime, duration or an array convertible to double.

Error in Untitled3 (line 26)

plot(th_2 , th_r)

[DGM]

th_2 and th_r are symbolic expressions. You could try to use fplot, but I don't know what you expect to get.

th_2 == th_3-110;
th_r == th_r+1; % this equation is the same as saying 0==1

[megan]

this code for position analaysis for 4bar mechanisim (rear windshield wiper mechanism ) , i want to get the plot of th_r and th_2 .

[Star Strider]

First, do not use global variables!

Second, we cannot solve problems that involve code that is ‘over the horizon’ and so out of view for us

[DGM]

I know you want a plot of th_r versus th_2. That's what the plot command said. To be fair, I wasn't very clear. What I said was:

• plot() doesn't handle symbolic expressions
• th_2 is a function of th_3 and could be used if th_3 were a parameter in an fplot() call
• but th_r is nonsense. What does it mean to plot 0==1? It's not a function of anything. It's a false assertion.

At least that's my impression of what's going on. Everyone is free to prove me wrong. It happens all the time.

[Rik]

Just in case this questions gets a strange edit as well:

What is the error? 1, fast

clc;
clear;
close;
global th_3 th_5  R L4 L5 L3 th_2  
R=5;
L3=19;
L4=44;
L5=31;
n=1; %num of rev
m=360*n; % num of dev of theta

acc=1;
a=1/acc;

th_r=linspace(0,2*pi ,m)
double th_2 
%syms th_3 th_5 th_r
eg1= ((asin((L3*sind(th_3)-R*sind(th_r))/L5)) - th_5) ;
eg2= ((acos(-(R*cosd(th_r)+L5*cosd(th_5)-L4)/L3)) -th_3)  ;
th_2 =( th_3-110)
th_r = th_r +a;

figure(1)
plot(th_2 , th_r)
grid on;

Message:

ans =

116 104 95 50

th_2 =

th_3 - 110

Error using plot

Data must be numeric, datetime, duration or an array convertible to double.

Error in Untitled3 (line 26)

plot(th_2 , th_r)

Answer 1

[Image Analyst]

What I get is

Error using -

Matrix dimensions must agree.

Error in test (line 18)

eg1= ((asin((L3*sind(th_3)-R*sind(th_r))/L5)) - th_5) ;

and that is because th_3 and th_5 are empty. They are empty because you declared them as global, which created them as empty arrays. You cannot add a non-empty array to an empty array.

[DGM]

I just deleted the globals line and uncommented the syms call.

[Image Analyst]

@DGM, so then what did you assign for th_3 and th_5 to get it to run past that line?

[DGM]

I didn't assign anything to them. I assumed that the error that the OP was getting wasn't obtained with the syms call commented out. All I did was replicate the error so that it could be observed.

[Image Analyst]

You never answered my questions in your duplicate post

https://www.mathworks.com/matlabcentral/answers/827600-how-to-do-code-with-2-equations-with-2-unknowns-and-an-angle-that-goes-from-0-to-360#comment_1517908

[megan]

i did

[DGM]

You're going to have to actually define the problem clearly for anyone to understand it. Label the points, describe the distance between said points. Once we can describe points by some unambiguous label, we can say which points we're trying to plot; more specifically, we can talk about the motion of one point versus another point.

You also need to define the constraints; which of these points are anchored with respect to the reference frame? All you have now is a four-bar linkage floating in space. Anything could move in any direction.

[Image Analyst]

So, which thread do you want to abandon, and which thread do you want to continue?

Also you didn't specify the rotation speed of each (I assume they're both the same), and the phase of one with respect to the other. Also, from your diagram, it looks like the windshield wipers go 360 degrees, which seems unrealistic since I think most go approximately 90 degrees. Why would a wiper go full circle???

[Image Analyst]

You said "theta z is gona 1 rev (from 0:360 deg)" which I took to mean "theta z is going to go through one revolution from 0 to 360 degrees). For that to happen I assumed the "x" wiper would have to go all the way around, 360 degrees.

Also you never answered my question about which thread you want to continue the conversation in (for the half day I have left before I'm off traveling until the end of the month), and didn't say what the phase difference between the wipers was. There is clearly a phase difference since your diagram does not show both wipers at the same angle at the same time. One is pointing to the left and one is pointing to the right.