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Anonymous Poster #1

Matlab Question

09/05/2019 8:20 AM

Dear sirs,

I want to have 9th day data from the following table.

Day 1 : 16

Day 3 : 40

Day 7 : 65

Day 14: 90

Day 28: 99.

How can I extract data of 9th day from Matlab?

Regards,

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#1

Re: Matlab Question.

09/05/2019 8:51 AM

What - as in 2/7 of (90-65) plus 65 equals 721/7?

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#2

Re: Matlab Question

09/05/2019 11:45 AM

First, you have to make an assumption about the data you do have. That assumption is that the data points are not a significant anomaly from a trend.

Second, one must make a subjective judgment what trend these data points lie upon; linear, periodic, exponential, polynomial, etc.

Third, fit a function using one of the curve fitting functions in Matlab appropriate for that curve.

Fourth, insert day 9 into the fitted function.

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#3

Re: Matlab Question

09/05/2019 11:53 AM

That looks like an exponential decay curve with a first-order time constant of about 4-5 days.

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#4
In reply to #3

Re: Matlab Question

09/05/2019 12:10 PM

It might be a fifth-order polynomial affected by a random hypergeometric probability distribution.

{I love to make things needlessly complicated, sometimes.}

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#9
In reply to #4

Re: Matlab Question

09/06/2019 3:34 AM

Yes. Er, um, what?

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#5
In reply to #3

Re: Matlab Question

09/05/2019 12:15 PM

Decay? Decay implies a negative slope.

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#6
In reply to #5

Re: Matlab Question

09/05/2019 12:21 PM

"1 minus (e to the minus k t)", then, not to be negative about it...

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#10
In reply to #3

Re: Matlab Question

09/06/2019 3:54 AM

Correction: 61/4 days.

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#7

Re: Matlab Question

09/05/2019 12:24 PM

I think what you are after is called interpolation, you want the value for December 9.

The function you want is interp1.

Let x be date: x=[1, 3, 7, 14, 28];

Let y be value: y=[16, 40, 65, 90, 99];

x1 = 9;

y1 = interp1(x,y,x1);

There are various options for interpolation.

Here is a help page:

http://matlab.izmiran.ru/help/techdoc/ref/interp1.html

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#8

Re: Matlab Question

09/05/2019 12:26 PM

73 is perhaps the closest integer estimate, maybe 74. PW's linear interpolation might not be a bad start, but the general curve indicates a bit more.

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