When discussing data and models for the Covid-19 Pandemic, one useful quantity to consider is P(t), the cumulative total number of Covid-19 cases confirmed up to and including day t. Note that we can set t = 0 to correspond to any given date. Although we might think of t as being an integer (i.e "day 1" or "day 10"), for the purpose of graphing and modeling the data we can think of time as a continuous variable, in which case t = 0 might correspond to midnight on a particular date. The total number of Covid-19 cases in the US confirmed between March 7, 2020 and March 17, 2020 are shown in Table 1 below.¹ Date in 2020 March 7 March 8 March 9 March 10 March 11 March 12 March 13 March 14 March 15 March 16 March 17 P(t) 190 253 323 444 606 813 1086 1419 1850 2432 3214 Table 1: Total number of Covid-19 cases in US, 2020. March 7 corresponds to t = 0. Covid-19 outbreaks in many countries, at least over short periods of time, appeared to show an exponential increase in the number of cases. In this case, we would model the growth of P(t) with the differential equation P' (t) = kP(t) where k is a constant. In this assignment, you are asked to investigate whether an exponential growth model is appropriate model for the data given. 1. First, graph the data using your favorite graphing tool and describe what you see. Does it look like exponential growth? Why or why not? (If you don't already have a favorite graphing tool, I recommend Desmos.)

Linear Algebra: A Modern Introduction
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Chapter7: Distance And Approximation
Section7.3: Least Squares Approximation
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When discussing data and models for the Covid-19 Pandemic, one useful quantity to consider
is P(t), the cumulative total number of Covid-19 cases confirmed up to and including day t.
Note that we can set t = 0 to correspond to any given date. Although we might think of t
as being an integer (i.e "day 1" or "day 10"), for the purpose of graphing and modeling the
data we can think of time as a continuous variable, in which case t = 0 might correspond to
midnight on a particular date.
The total number of Covid-19 cases in the US confirmed between March 7, 2020 and March
17, 2020 are shown in Table 1 below.1
Date in 2020
March 7
March 8
March 9
March 10
March 11
March 12
March 13
March 14
March 15
March 16
March 17
P(t)
190
253
323
444
606
813
1086
1419
1850
2432
3214
Table 1: Total number of Covid-19 cases in US, 2020. March 7 corresponds to t = 0.
Covid-19 outbreaks in many countries, at least over short periods of time, appeared to
show an exponential increase in the number of cases. In this case, we would model the growth
of P(t) with the differential equation
P' (t) = kP(t)
where k is a constant. In this assignment, you are asked to investigate whether an exponential
growth model is appropriate model for the data given.
1. First, graph the data using your favorite graphing tool and describe what you see. Does
it look like exponential growth? Why or why not? (If you don't already have a favorite
graphing tool, I recommend Desmos.)
Transcribed Image Text:When discussing data and models for the Covid-19 Pandemic, one useful quantity to consider is P(t), the cumulative total number of Covid-19 cases confirmed up to and including day t. Note that we can set t = 0 to correspond to any given date. Although we might think of t as being an integer (i.e "day 1" or "day 10"), for the purpose of graphing and modeling the data we can think of time as a continuous variable, in which case t = 0 might correspond to midnight on a particular date. The total number of Covid-19 cases in the US confirmed between March 7, 2020 and March 17, 2020 are shown in Table 1 below.1 Date in 2020 March 7 March 8 March 9 March 10 March 11 March 12 March 13 March 14 March 15 March 16 March 17 P(t) 190 253 323 444 606 813 1086 1419 1850 2432 3214 Table 1: Total number of Covid-19 cases in US, 2020. March 7 corresponds to t = 0. Covid-19 outbreaks in many countries, at least over short periods of time, appeared to show an exponential increase in the number of cases. In this case, we would model the growth of P(t) with the differential equation P' (t) = kP(t) where k is a constant. In this assignment, you are asked to investigate whether an exponential growth model is appropriate model for the data given. 1. First, graph the data using your favorite graphing tool and describe what you see. Does it look like exponential growth? Why or why not? (If you don't already have a favorite graphing tool, I recommend Desmos.)
2. As we know from class, the solution to the differential equation above is P(t) = P₁ekt.
Determine a value for the constant k that you think does a good job at describing the
data. Note that there are many different ways to do this, so be sure to discuss in detail
what you did and why you did it that way. Graph your exponential model along with
the data and comment on how well (or not) it seems to be modeling the data.
3. On March 27 (t = 20), there were 58,330 total cases in the US. Compare this number to
the model's prediction for that day. On April 30 (t = 54) there were 988,487 total cases.
Compare this number to the prediction for that day. If there are discrepancies between
the predicted values and the actual values, comment on possible reasons.
4. One way to better understand how close the data are to exponential is to look at the
quantity
1 dp
P dt
If the growth is truly exponential then this would be a constant. On the other hand,
if it's not quite constant, that's a clue that growth is not quite exponential. Since the
derivative of P can be estimated by the average rate of change over one day, we can
approximate
1 dp
P dt
P(t+1) - P(t)
P(t)
For the data given, make a graph of the quantity on the right hand side over time. Does
it appear to be constant?
Transcribed Image Text:2. As we know from class, the solution to the differential equation above is P(t) = P₁ekt. Determine a value for the constant k that you think does a good job at describing the data. Note that there are many different ways to do this, so be sure to discuss in detail what you did and why you did it that way. Graph your exponential model along with the data and comment on how well (or not) it seems to be modeling the data. 3. On March 27 (t = 20), there were 58,330 total cases in the US. Compare this number to the model's prediction for that day. On April 30 (t = 54) there were 988,487 total cases. Compare this number to the prediction for that day. If there are discrepancies between the predicted values and the actual values, comment on possible reasons. 4. One way to better understand how close the data are to exponential is to look at the quantity 1 dp P dt If the growth is truly exponential then this would be a constant. On the other hand, if it's not quite constant, that's a clue that growth is not quite exponential. Since the derivative of P can be estimated by the average rate of change over one day, we can approximate 1 dp P dt P(t+1) - P(t) P(t) For the data given, make a graph of the quantity on the right hand side over time. Does it appear to be constant?
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