Running simulation help; Left and right sides have uneven number of elements?

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Lee 2022-2-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1659300-running-simulation-help-left-and-right-sides-have-uneven-number-of-elements

评论： Image Analyst 2022-2-28

Hi! I'm looking for some homework help. My task is to run a simulation on caterpillars in a tree. I have been given two equations that show the way in which the caterpillars exist in the tree.

dN = R * N(t-1) * (1 - N(t-1)/Ntot)
    N(t) = N(t-1) + dN * dT;

Where:

R= rate of reproduction

Ntot=total capacity that the tree can support

N=Number of caterpillars

I am looking to run the simulation and then plot the conditions over time.

I have been given some initial conditions:

25 timesteps, interval of .1, R=5, Ntot=100 and the starting amount of caterpillars is N=10.

I have the code written out how I believe it should end up looking but I recieve the error "Unable to perform assignment because the left and right sides have a different number of elements"

I'm not really sure what part this is refering to and I don't know how to fix it. Any help appreciated!

nT=25 %timesteps
dT=.1 %interval
%variables
N=zeros(nT,1);
R=zeros(nT,1);
Ntot=zeros(nT,1);
%initial conditions
P(1)=0;
N(1)=10;
R(1)=5;
Ntot(1)=100;
%run the simulation using initial conditions and plot (without predators)
figure
hold on
for t=2:nT
    dN = R * N(t-1) * (1 - N(t-1)/Ntot);
    N(t) = N(t-1) + dN * dT;
    plot(dN,N(t))
end

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Answer 1

Image Analyst 2022-2-26

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https://ww2.mathworks.cn/matlabcentral/answers/1659300-running-simulation-help-left-and-right-sides-have-uneven-number-of-elements#answer_905425

Since R is a vector, dN is a vector. N is a vector but N(t) is just one element of a vector. However since dN is a vector, you have a vector on the right hand side and you're trying to put that whole vector into a single element. Can't do that. A single element at N(t) can take only a single number.

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Lee 2022-2-28

How do I fix that? I don't know that I understand what you're saying

Image Analyst 2022-2-28

Just take the semicolons off the ends of the lines and step through it a line at a time, and then you will understand. See the link below if you don't know how to debug:

Debugging in MATLAB | Doug's MATLAB Video Tutorials

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