how to see x and y cordinate in the plot beyond its end point?

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satish thapaliya 2012-11-21

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I have a matlab plot containing value of x from 5 to 25. I want to find the y value corresponding to 3 at x axis but I can't use data cursor to indicate that point. What option can help me with it?

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Answer 1

Harshit 2012-11-21

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HI Satish, If you dont have any information about the values beyond 5 and 25 then you have to extrapolate. Well the type of extrapolation depends on your plot. If it is a line linear extrapolation will work. Otherwise get the correct type of extrapolation.

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satish thapaliya 2012-11-21

How does it work? could you make a bit clearer with some examples?

Harshit 2012-11-21

Well one idea is to use polyfit to get curve corresponding to it. Only thing is to get the parameter of this function. Then evaluate x(3) on this polynomial. Jan's answer is one more approach.

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Answer 2

Jan 2012-11-21

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You have y-values for the x-values 5 to 25. Now you want the y-value for x==3. Obviously this is not possible directly. There is no such corresponding value.

If the values are predictable, you can "extrapolate". Example: If all points build a line, you can expect, that the value of x==3 is on this line also. See "help interp1" with the "extrap" flag. But if the values are more random or follow a high order polynomial, a prediction of a value outside the defined interval is more or less guessing.