Array of x and y values. Find value of y when x=0, how?

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Elin Berntsson 2017-11-27

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评论： KL 2017-11-28

Hello. I have an assignment in school, where we got an array with x and y values to plot.

Time=[0.5:0.5:5];

A=[1.2 0.73 0.45 0.27 0.16 0.11 0.06 0.035 0.022 0.013];

plot(Time,A) gives me a graph but I need the value of A when Time=0;

I don't have a function or equation, only these values. So when Time=0, what is the value of A?

I'm thinking that some kind of y-intercept thing can be the solution?

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Answer 1

KL 2017-11-27

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You might want to use interp1,

read: https://de.mathworks.com/help/matlab/ref/interp1.html

Hint: For your case, 0 lies outside the range you've got, so you might want to extrapolate.

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Elin Berntsson 2017-11-27

Yeah so I've been trying a few times now but i don't think I'm using the interp1 function right.

this is my code so far:

Time=[0.5:0.5:5];

A=[1.2 0.73 0.45 0.27 0.16 0.11 0.06 0.035 0.022 0.013];

plot(Time,A)

A0 = interp1(A,0,linear,extrap)

it's not working and I still kinda don't understand the description that mathworks has for it.. Thankful for your help!

KL 2017-11-28

I agree with the cyclist. In your question you say ...I don't have a function or equation, only these values... and looks like you do have one.

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Answer 2

the cyclist 2017-11-27

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Strictly speaking, it is not possible to know what the value of A is at Time=0, given only this information. An infinite number of functions could fit these data, and give different values at Time=0. Or maybe Time=0 is an asymptote, and the fit line never crosses it.

Do you have any other relevant info that you have not shared?

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Elin Berntsson 2017-11-27

Well yes I have the two arrays of values, time and A(time). I also have an equation;

A(time)=A0*exp(-k*time)

I don't have a value for k, that is also something that i should calculate. The question says: Calculate A0 (value of A when the time=0) and k by plotting the values in the arrays;

Time=[0.5:0.5:5];

A=[1.2 0.73 0.45 0.27 0.16 0.11 0.06 0.035 0.022 0.013];