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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What is the approach used to interpolate value and how to fix it.

This question is related to the calculation of sunrises and sunsets. There is a JavaScript library https://github.com/Fabiz/MeeusJs that is based on the book Astronomical Algorithms by Jean Meeus. I guess the code of the library mostly is fine but I…
Raf
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Inverse interpolation Newton's base formula proof

I'm recently doing Numerical Analysis, more specifically about interpolation. In my book (A pretty old book which was not written in English), the author gives the following algorithm to find the solution of $f(x) = y$, where $y$ is given, $f(x)$ is…
Bakkune
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Non-linear interpolation. (1D Perlin Noise)

In this document (http://webstaff.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf) about Perlin (and Simplex) Noise you can find an explanation about 1D Perlin Noise (at the top). https://i.stack.imgur.com/acGyZ.png For a given point x somewhere…
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Interpolate to 3D functions

Hy, In math classes, I've learned that given some points in 2D space: a(1,2), b(7,3), c(8,5),... You can find an equation that goes through these points (using interpolation). Now I was wondering if the same is possible for 3D points?…
genz
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Interpolation of three positive values at 0, 1 and 2 by a polynomial with non-negative coefficients

I am asking myself the question: Let $ y_0, y_1, y_2 $ be positive real numbers. Is there always a polynomial $ f $ with non-negative real numbers as coefficients which satisfies $ f( i ) = y_i $ for $ i = 0, 1, 2 $? Thanks for thinking about it.
diddy
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Cubic Spline Interpolation - Constructing the Matrix

Interpolate a cubic spline between the three points $(0, 1), (2, 2) \text{ and } (4, 0).$ I'm trying to understand how to interpolate a given set of points using cubic splines with the help of this solved example. I don't quite get how they…
Monika
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What's the Vandermonde matrix of 4 points?

I'm learning about Vandermonde matrix to get monomial basis. Suppose I have 4 points $(-1, 2),~ (0,7),~ (1,22) $ and $ (2,71)$ I was taught how to create the Vandermonde matrix using arbitrary numbers: $$\begin{bmatrix}1 &&x^1&& x^2 &&x^3&&\dots&&…
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Interpolation of a 3D curve in space

I'm doing a curious exercise. I have to find a method to interpolate the following ballistic trajectory in 3D space: $$\left\{\begin{matrix} x(t) = \frac{v\cos(\phi)\cos(\beta)}{k}(1-e^{-kt})+d_{0}\cos(\alpha)\\ y(t) =…
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How to recalculate a lerp percentage value, so that it returns the same value, even when the max lerp value is adjusted?

I currently have a lerp function, which is $$ y = p \cdot x_2 + (1 - p) \cdot x_1, $$ where $x_1$ is the min lerp value, $x_2$ is the max lerp value, $p$ is the percentage to lerp between $x_1$ and $x_2$, in a $0.0$ to $1.0$ format, and $y$…
Grifyon
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Interpolating multivariable functions

Assume I have two functions, $f_1$ and $f_2$, that both depend on $x$ and $y$, so that $f_1(x,y)$ and $f_2(x,y)$. I don't know the exact functions, but know values of each function at some points (actually, any points I want). So, for example, let's…
Marcelo
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Proof involving interpolating polynomials

Let $f$ be sufficiently differentiable on $[a,b]$ and write $a=x_0$, $x_1 = \frac{a+b}{2} = x_0+h, x_2 = b = x_1+h$. Prove that $a)$ there exists a cubic polynomial $q$ such that $f(x_i) = q(x_i)$, $i=0, 1, 2$, $f'(x_1) = q(x_1)$, and that $b)$…
mXdX
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Even Functions for RBFs

I have been searching the literature for a while on this and cannot find a clear explanation. This relates to Radial Basis Function Interpolation but I think it applies more generally. I have a square matrix $r$ of interpoint distances for a sample.…
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Combination of interpolation types for multivariate interpolation

I have a N-dimensional dataset, for which I need to apply multivariate interpolation. Is there a possible way to use different kind of interpolation methods in different dimensions? I considered to do this since I want to reduce the overall…
jochim
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2d interpolation using derivatives

I have four points on a rectangular grid $(x_1,y_1)$, $(x_1,y_2)$, $(x_2,y_1)$ and $(x_2,y_2)$. I also have the value of a third variable $z$ at each of these points, as well as the partial derivatives $\frac{\partial z}{\partial x}$ and…
Adrian
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Solve for missing values using linear interpolation

I have been tasked with trying to find a launch angle for a pumpkin launcher for a competition with a club at school! I am given the following data in a table and my goal is to find the launch angle to achieve a certain range given a distance and…