i have two array x=[1 6 8 9],y=[3 6 9 14],then i plot (x,y) in matlab. i have no linear equation of x,y. i have only above array of x and y. if value of x is 4 then what is the value of y. is it possible using logic?

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vipul utsav 2012-11-29

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i have two array x=[1 6 8 9],y=[3 6 9 14],then i plot (x,y) in matlab. i have no linear equation of x,y. i have only above array of x and y. if value of x is 4 then what is the value of y.

is it possible using logic?

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vipul utsav 2012-11-29

'interp1' this is inbuilt function ,so i just want logic behind it

Azzi Abdelmalek 2012-11-29

What result are you expecting?

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Matt Fig 2012-11-29

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x=[1 6 8 9];
y=[3 6 9 14];
interp1(x,y,4,'linear')

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vipul utsav 2012-11-29

yes i read help,but for 11 inter11 doesn't work. and for 4 it is work. 11 is outside of maximum value in x.

Matt Fig 2012-11-29

编辑：Matt Fig 2012-11-29

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If you read the help, you would see there is an extrapolation option. When you want to look at values outside the range, you are extrapolating. You should also know that extrapolating is usually something one does not want to do for real applications.... especially for so sparsely populated data as this!

interp1(x,y,11,'linear','extrap')

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Jan 2012-11-29

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编辑：Jan 2012-11-29

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There is an infinite number of possible values: You can e.g. define an infinite number of polynomials through these points. And there are much more functions than only polynomials.

Therefore this problem cannot be solved, when there are no further restrictions.

One workaround would be to choose 19. This is not really serious, but fast and it solves the question as good as any other value also. The choice of 19 is explained in Carl E. Liderholm: "Mathematics Made Difficult", 1972:

Each sequence of natural number can be continued by 19.