plot different parts of vector

I´ve got a vector M(1x80) and would like to plot four different graphs (graph 1 equals values 1:20, graph 2 values 21:40, ...) and have a name of each of them in the legend (including a trendcurve):

I thougt of a loop like that:

for i = 1:20:80

plot(M3(i);

legend('Graph 1');

end

Can you tell me where the error is?

Thanks a lot for helping me!

Answer 1

[Sriram Tadavarty]

Hi Robin,

The following code will provide what you are looking for

M3 = rand(1,80);
j = 1;
str = [];
for i = 1:20:80
    hold on
    plot(M3(i:19+i)); % Update this to have 20 values, which is fixed to 1 in your code
    str = [str ["Graph " + num2str(j)]]; % To have different legend for each plot through string array
    j = j+1;
end
legend(str)

Hope this helps.

Regards,

Sriram

[Robin Strak]

Hi Sriram,

thanks a lot for your great answer - that helped a lot!

The only problem I´m having is that it now opens up 4 different windows instead of putting all of them in one figure. Obviously I will need a "hold on", but I can´t find the correct position to fix it.

Regards,

Robin

[Sriram Tadavarty]

Hi Robin,

I couldn't get that all the plots must be in same figure from the question. Updated the answer for it. Please have a look and let me know.

Regards,

Sriram

[Robin Strak]

Thanks, Sriram, it works now :)

Maybe you could help me with a further question:

As I added a trendline to every graph I wanted the graph and the trendline to have the same colour. I tried to come up with 4 different colours in "col" , add them to the plots and increment them after every loop, but Matlab doesnt like the "k" argument in colour.

k =1;

col = {'g', 'y', 'c', 'm'};

for i = 1:20:80

plot(M_3(i:19+i), col(k));

str = [str ["Graph " + str(j)]];

c_rms = polyfit(time,M_3(i:19+i),1);

y_est = polyval(c_rms,time);

hold on

plot(time,y_est, col(k) 'LineWidth',2)

j = j+1;

k = k+1;

Do you know what I need to change?

[Sriram Tadavarty]

Hi Robin,

Please do accept the answer, if helped.

Here, col is the cell array and it need to be accessed through curly brackets {} rather than open bracket (k).

I am not sure what the variable time is.

Use col{k} instead of col(k), it solves the issue. Here is a partial code

col = {'g', 'y', 'c', 'm'}; 
for i = 1:20:80
    plot(M_3(i:19+i), col{k}); 
    str = [str ["Graph " + num2str(j)]]; 
    c_rms = polyfit(1:20,M_3(i:19+i),1);
    y_est = polyval(c_rms,1:20);
    hold on
    str = [str ["Polyfit " + num2str(j)]];
    plot(y_est, col{k}, 'LineWidth',2)
    j = j+1;
    k = k+1;
end
legend(str)

This should provide some insights of how to solve this. I suggest you to start a new question, if there is any other problem.

Thanking you

Regards,

Sriram