Just looks roughly reasonable shapes for the diff equations and experience of what these kind of things typically look like.

I've not ever formally done SIR models, but Covid has made experts of us all...

Reply 4

Great444

Original post by DFranklin

Thanks

Reply 5

Great444

Original post by Great444

Thanks

Original post by DFranklin

It looks reasonable. It's mu, not meow, by the way!

How do I figure out the steady states from the graph?

Reply 6

DFranklin

Original post by Great444

How do I figure out the steady states from the graph?

Just read them off, surely? (You might want to run over a longer period).

Are you sure you're not supposed to get them from the diff eqns? At steady state the derivatives would all be 0 and you get some simultaneous equations to solve.

Reply 7

Great444

Original post by DFranklin

Are you sure you're not supposed to get them from the diff eqns? At steady state the derivatives would all be 0 and you get some simultaneous equations to solve.

Yes I am which I did , but I have also to get them from the graph and compare between them, how do I get them from the graph ?Just read them off, surely? (You might want to run over a longer period).

Reply 8

DFranklin

Original post by Great444

Yes I am which I did , but I have also to get them from the graph and compare between them, how do I get them from the graph ?Just read them off, surely? (You might want to run over a longer period).

Was going to be a bit more explicit and found myself doubting your graph after all.

Shouldn't S+I+R always sum to 1? (Looking at the DEs it seems the sum of the 3 derivatives should be 0).

Reply 9

Great444

Original post by DFranklin

Was going to be a bit more explicit and found myself doubting your graph after all.

Shouldn't S+I+R always sum to 1? (Looking at the DEs it seems the sum of the 3 derivatives should be 0).

Check now

sir4.GIF37.3KB

Reply 10

DFranklin

Original post by Great444

Check now

Still doesn't look right. If S is almost zero dS/dt should be mu (and so S should be growing).

Note that I'm merely eyeballing your charts. I'm not going to do my own simulation just to troubleshoot yours.

Reply 11

ghostwalker

Original post by DFranklin

@Great444 for info.

wadr, I'd run the simulation on Excel and got identical results to the OP.

Although S gets close to zero, the

\beta S I

term of dS/dt is of the same order of magnitude as

\mu

at that point.

(edited 2 years ago)

Reply 12

Great444

Original post by DFranklin

Good idea, I'm waiting for the result :smile:

I think it's right but not sure 100%

Reply 13

Great444

Original post by ghostwalker

@Great444 for info.

wadr, I'd run the simulation on Excel and got identical results to the OP.

Although S gets close to zero, the

\beta S I

term of dS/dt is of the same order of magnitude as

\mu

at that point.

Does this mean it's correct?

Reply 14

ghostwalker

Original post by Great444

Does this mean it's correct?

Probably, or we both made the same mistake.

Reply 15

ghostwalker

Original post by Great444

Does this mean it's correct?

Although it shouldn't effect the steady state values, changing the step size does impact the graphs.

E.g. h=0.1 gives

Untitled.jpg65.3KB

Reply 16

Great444

Original post by ghostwalker

Probably, or we both made the same mistake.

I don't think so.
Any idea about this ? Using suitable sources find a disease that you believe can be modelled accurately with the SIR model with demography.
Thank you

Reply 17

ghostwalker

Original post by Great444

I don't think so.
Any idea about this ? Using suitable sources find a disease that you believe can be modelled accurately with the SIR model with demography.
Thank you

None. Think you might need a biologist on that one.