How do I interpolate the value in certain data point by array of known points?

Question

I have known data points and their values described as arrays, speed and power

speed = [2, 6, 8, 10, 12]
power = [200, 450, 500, 645, 820],

I want to estimate the power value that corresponds to speed value (e.g. 7) that is not listed within source array (2 through 12).

I.e. I am seeking a way to perform interpolation

Answer 1

The simplest way to do that is to perceive your power-from-speed dependency as a collection of lines and assuming your target point falls between two known points of a certain line, calculate the value.

E.g. you may do the following:

const speed = [2, 6, 8, 10, 12], power = [200, 450, 500, 645, 820]
  
const interpolate = (xarr, yarr, xpoint) => {
 const xa = [...xarr].reverse().find(x => x<=xpoint),
   xb = xarr.find(x => x>= xpoint),      
   ya = yarr[xarr.indexOf(xa)],      
   yb =yarr[xarr.indexOf(xb)]  
 return yarr[xarr.indexOf(xpoint)] || ya+(xpoint-xa)*(yb-ya)/(xb-xa)
}

console.log(interpolate(speed,power,7))

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