Questions tagged [interpolation]

Questions on interpolation, the estimation of the value of a function from given input, based on the values of the function at known points. It is necessary because in science and engineering we often need to deal with discrete experimental data.

Interpolation is a useful mathematical and statistical tool used to estimate values between two points on a line or curve.

What Is Interpolation?

Interpolation is the process of deriving a simple function from a set of discrete data points so that the function passes through all the given data points (i.e. reproduces the data points exactly) and can be used to estimate data points in-between the given ones.

To help us remember what it means, we should think of the first part of the word, 'inter,' as meaning 'enter,' which reminds us to look 'inside' the data we originally had.

Applications: This tool, interpolation, is not only useful in statistics, but is also useful in science, business or any time there is a need to predict values that fall within two existing data points. It is also used to simplify complicated functions by sampling data points and interpolating them using a simpler function. In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points. In engineering and science, one often has a number of data points, obtained by sampling or experimentation, which represent the values of a function for a limited number of values of the independent variable. It is often required to interpolate, i.e., estimate the value of that function for an intermediate value of the independent variable.

The details, techniques, and precise meaning of interpolation depend heavily on the sub-discipline of mathematics, therefore you are encouraged to use additional subject tags such as , , , or when appropriate.

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1-D Interpolation between any number of points

I'm looking for an algorithm which will allow me to calculate outputs for any given input instead of just the few ones I'm given in advance. The input is a number from interval $0 - 100$ representing a percentage. I'm given a few of the desired…
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Interpolation with constant rate of increase

Let's assume we have data for two points ( X_Left -> Y_Left, X_Right -> Y_Right ), and we break the interval between X_Left, and X_Right, into equaly distant sub intervals. In case I wanted to do a linear interpolation, for either of the equaly…
Joquim
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Approach for efficient interpolation of sum of polynomials?

I'm trying to find an approach for recovering the coefficients of a polynomial (the "sum polynomial") that is the sum of a bunch of polynomials. The application is to build a secure protocol for adding up secret inputs, based on Shamir's secret…
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How does one linearly interpolate two equations?

Was looking at this video https://youtu.be/60VoL-F-jIQ?t=213 and a linear interpolation between two equations is mentioned. I don't understand how one linearly interpolates two equations. The video shows the following 2 equations and a 3rd one which…
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Error in Linear Interpolation.

I am linear interpolating two points $(x_0, f_0)$ and $(x_1, f_1)$. Using Taylor Expansion. $$f(x_0+\Delta x) = f(x_0) + f'(x_0) \Delta x + \frac{1}{2!} f''(x_0) (\Delta x)^2+\cdots$$ In the textbook, it is given that $$f(x) =…
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Linear interpolation accuracy

I am trying to create a formula to calculate x for given y. I have 74 samples. I tried to do it with linear interpolation. However, the accuracy isn't good. These are my samples: x: 1 , 1.5, 2, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5,…
Bowman
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$C^2$ Smoothing of absolute value

I am looking for a function $f\colon \mathbb{R}\to\mathbb{R}$ such that $$g(x)=\begin{cases} f(x), &\text{if }| x|
vv33d
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How to interpolate from rotated rectangle / grid?

I have a grid made from rectangles, rotated by an arbitrary angle. Each point of the grid is defined by a GPS coordinate vector of the form $(lon, lat)$ and has an elevation assigned. Now, I have an arbitrary point $P$ defined by a vector $(lon,…
TheEagle
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Prove that this function interpolates function in $x_0, x_1,..., x_n$

Let $q\in \prod_{n-1}$ be interpolation polynomial for $x_1,...,x_n$ and $p\in \prod_{n-1}$ be interpolation polynomial for $x_0,...,x_{n-1}$. Show that function $$N(x)=q(x)\left( 1+\frac{x_n-x}{x_0-x_n}\right) - \frac{x_n-x}{x_0-x_n}p(x)$$ is…
Awerde
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Cubic interpolation derivation

I have seen the following cubic interpolation formula in multiple books on multigrid: $$f(x) = -\frac{1}{16}f(x-3h) + \frac{9}{16}f(x-h) + \frac{9}{16}f(x+h) -\frac{1}{16}f(x+3h).$$ Applying the above to some vector $v_i = f(x + (1+2i)h)$, such that…
lightxbulb
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Offset bell curves that sum to a fixed value

I'm in need of a well studied bell curve function $f(x)$ that satisfies the following equation: $\exists P,\!C \; \forall x \:\left(\sum_{i=-\infty}^{\infty}{f(x+i P)}\right)=C$ That is; an infinite set of them offset by some fixed interval sums…
BCS
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Estimate an upper bound for interpolation polynomial

Given a function f and an unique interpolation polynomial P, we can say that for every x there is a r so that $f(x)-P(x)=\frac{\omega(x)f^{n+1}(r)}{(n+1)!}$ where r is in the smallest interval $[x_0,...x_n,x]$ that contains x and all support points…
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Is the wikipedia bilinear interpolation example wrong?

On the Wikipedia Bilinear interpolation page there is this numerical example. I am talking about the example with this image. There I see $I_{20,14.5}=\frac{15-14.5}{15-14} \cdot 91 + \frac{14.5-14}{15-14} \cdot 210$ Should not we swap $91$ and…
O. Altun
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Interpolation error: Prove that $|f(t)−p(t)| \leq \frac{1}{24} \underset{\xi \in [t_0,t_2]}{\max}|f^{(4)}(\xi)||(t−t_0)(t−t_1)^2(t−t_2)|$

Let $f \in \mathcal{C}^4(\mathbb{R})$ be a real valued function, let $t_0< t_1< t_2$ be real numbers and $p$ is a polynomial of degree $≤3$, which satisfies $p(t_j)=f(t_j) , \ j= 0,1,2$ and $p'(t_1) =f'(t_1)$. a) Prove that for $t \in…
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Why 2D linear interpolation formula sums the initial point's y component?

$$y=y1+(x-x1)\frac{y2-y1}{x2-x1}$$ https://matthew-brett.github.io/teaching/linear_interpolation.html I've seen this formula in multiple places and I'm wondering why do we need to multiply the distance between $x$ and $x1$ to the slope and add it to…