## 03-06 Infection Model Solution

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This answer would simply lead to a decay of the number of infectious persons
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no matter what the rate of change is a negative factor times the current value.
• 0:10 - 0:12
This doesn't make sense
• 0:12 - 0:17
With this answer, the rate of change which depend only on the number of susceptible persons.
• 0:17 - 0:21
It would not matter to the rate of change of the number of infectious persons
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whether we started with 1 or 10 or 1 million infectious persons.
• 0:27 - 0:33
This doesn't make sense. So we have to have a solution that incorporates both quantities.
• 0:33 - 0:39
The number of susceptible persons and the number of infectious persons. So what about that ratio?
• 0:39 - 0:44
This would mean that if the number of infectious person is low, this ratio is high.
• 0:44 - 0:49
We divide by a small number and the rate would be high which again doesn't make sense.
• 0:49 - 0:52
And there is another reason why this doesn't makes sense,
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the unit would be 1/days times persons/persons.
• 0:57 - 1:05
This canceled and unit of the result is 1/days but what we need is persons per day,
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so this cannot be true for several reasons.
• 1:08 - 1:12
This is what is left and it makes sense. Let's look at the units.
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A number divided by days and persons, times persons squared.
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What we are left with is person per day, that's what we need and this product has the right behavior.
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If we increase the number of infectious persons, we increase that rate.
• 1:28 -
We have more encounters. That makes sense.
Title:
03-06 Infection Model Solution
Team:
Udacity
Project:
CS222 - Differential Equations
Duration:
01:31
 Amara Bot edited English subtitles for 03-06 Infection Model Solution Gundega added a translation

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