Why do I received Error using Plot?

Dear Matlab Expert!

I am a student and still new to Matlab. Currently, I had been learning the COVID-19 model and I would like to learn the coding of this model. In order to learn the coding, I had downloaded the "SIRD model for COVID-19 outbreaks" coding that I found in the File Exchange and tried to run the coding. But when I run the sird_covid_run_ita.m, I got this error :

Error using plot
Vectors must be the same length.
Error in sird_covid_run_ita (line 121)
plot(data_long,I,'-r',date,I_exp,'r*',data_long,R,'-g',date,R_exp,'gd');

Can anyone help me? What is meant by the Vectors must be the same length? I did tried many times to fix the error but it is quite hard to do so as I am still new with the Matlab. I would be really, really grateful if anyone can help me run this coding without error.

Thank you very much and I appreciate your help so much :)

[dpb]

"What is meant by the Vectors must be the same length?"

Exactly that -- the "X" and "Y" vectors to plot must have the same number of elements -- and in the command line above at least one pair of those isn't for your case for some reason...

The command

plot(data_long,I,'-r',date,I_exp,'r*',data_long,R,'-g',date,R_exp,'gd');

is trying to plot four separate lines

plot(data_long,I    ,'-r', ...
     date     ,I_exp,'r*', ...
     data_long,R    ,'-g', ...
     date     ,R_exp,'gd');

rewriting the format of the command to separate the four.

I and R are trying to be plotted against data_long and I_exp and R_exp are trying to be plotted against data, so those two pairs will have to have same number of values in each.

Which is the offending you'll have to see -- set a breakpoint in the function just before the plot() command and look at each of the variables in turn to see how long they are -- at least one will be different. Now, why, would take going to see just how they're being computed to see where there must be some sort of logic error.

Is there a sample dataset that is with the download? Does it not run successfully?

[William Rose]

@Sofea Irene,

I cannot run the code since I am currently using Matlab 2016. This old version does not suport some of the commands in the script. I hope to have my regular computer back soon.

The error message indicates that the number of x-values and the number of y-values are not equal. They must be equal for plot() to plot the data set.

I have looked at the code on the File Exchange site. I see you posted your question there also. The error occurs in figure 6. The command that fails is

plot(data_long,I,'-r',date,I_exp,'r*',data_long,R,'-g',date,R_exp,'gd')
hold on

The command above plots four data sets. You can look in the list of variab;les in the "Workspace" pane of the Matlab window, to determine the length of data_long and I and R (they should all be the same length), and the length of date, I_exp, and R_exp (they should all be the same length).

You can also try dividing the plot() command above into 4 separate commands.

plot(data_long,I,'-r')  %
hold on
plot(date,I_exp,'r*')
plot(data_long,R,'-g')
plot(date,R_exp,'gd')

This will let you determine which plots fail and which plots work. You can comment out the plots that do not work. This will allow the script will run to completion.

Good luck.

[Image Analyst]

I don't get that error when I run the m-file in the URL you gave. I get this:

Error using split

First argument must be text.

Error in test6 (line 7)

date=(split(data{3:end,1},'T'));

So if you're getting past that you must have fixed the file somehow. Can you attach your actual m-file?

If you have any more questions, then attach your data and code to read it in with the paperclip icon after you read this:

TUTORIAL: How to ask a question (on Answers) and get a fast answer

[Sofea Irene]

Hi @Image Analyst @William Rose @dpb

Thank you for aswering my question. I still figure out the error but my lecturer just gave me another coding for me to study as this coding is quite complicated.

I would like to apologise for the late reply as I did'nt get the notification and still new with this website.

Thank you very much and I appreciate your help so much :)

[William Rose]

@Sofea Irene, you are welcome. Good luck with your work.

Answer 1

[William Rose]

@Sofea Irene, I have moved my comment to be an answer, as I originally intended, and I have added to it.

[edit: correct spelling errors]

Your error message indicates that the number of x-values and the number of y-values are not equal. They must be equal for plot() to plot the data set.

The error occurs in figure 6. The command that fails is

plot(data_long,I,'-r',date,I_exp,'r*',data_long,R,'-g',date,R_exp,'gd')

The command above plots four data sets. You can look in the list of variables in the "Workspace" pane of the Matlab window, to determine the length of data_long and I and R (they should all be the same length), and the length of date, I_exp, and R_exp (they should all be the same length). When I run the code, I do not get this error. I don't know why you get the error, and I do not. For me, data_long and R and I are all 201 elements long. For me, date and I_exp and R_exp are all 935 long.

I had to make several adjustments to sird_covid_run_ita.m, to get it to run. You got to figure 6 before you had an error, so you did better than me!

I got an error when the script tried to download the data file from the web. Therefore I downloaded the text file before running the script, and commented out the lines in the script that fetch the file online. Now my version of the script reads the text file from my hard drive. I am currently using Matlab 2016a, which does not support the split() command. I hope to have my regular computer back soon, with up-to-date Matlab. So I wrote a work-around for the missing split() command. After these adjustments, the script has an error on figure 3. The error was "index exceeds matrix dimensions". This occurs because the code was written when they had less than 200 days of data, so they stopped the simulation at 200 days. Now they have over 900 days of data, but the simulation still stops at 200 days. This causes problems with figures 3, 4, and 5. I fixed these errors. Then the plot command in figure 6, which caused an error for you, ran fine for me. I did get an error later in figure 6, with the xlim() command. I fixed it by commenting out that command.

In case you do not know: by "commenting out the command", I mean that I placed a % character at the start of the line, to turn the command into a comment.

Then figure 8 works, but there is an error on figure 7, which is plotted after figure 8. The error is

Error using sird_covid_run_ita (line 167) (my line numbers are different now)

Subscript indices must either be real positive integers or logicals.

This error happens because repr_vect_mean is an empty vector. It is empty because the reproduction coefficient is never greater than about 10^-10.

-----

The model is failing. Figures 3, 4, and 5 show zero infections for the first 200 days. (They only evaluate the model for the first 200 days.)

----------

@Sofea Irene, you picked a very complicated program to get started in Matlab.

Good luck.

[William Rose]

@Sofea Irene,

I am ataching my version of the script. As I noted above, this version plots figures 1-6 and 8. Then it has an error on figure 7, for the reason I explained. To run my version of the code, you also need a local copy of the data file, which I am also attaching.

When I run my version of the script, figures 3 through 6 show zero infections and zero deaths for the 200 simulated days. This is unrealistic, and this is why I say the model is failing. Perhaps the model formulation cannot adapt to the existence of 935 days of data. The plot commands for figures 3-6 in the File Exchange version of the script indicate that the authors did not anticipate what would fail when the data extended beyond 200 days.