What is Lagrange Interpolation? An Overview

What is Lagrange Interpolation?

Lagrange interpolation theorem may be used to generate a polynomial that passes over a group of points and takes certain values randomly. The formula for nth-degree polynomials is given by this theorem (x) if f(x) is known at discrete points xi, I = 0, 1, 2,... In addition, it illustrates the theorem in a constructive way. Lagrange's theorem may be used for both equally and unequally spaced locations. This indicates that the xs values are not uniformly distributed. It is a technique for estimating a mathematical expression that uses any approximate state for the independent variable. Interpolation is mostly used to identify what additional data may exist outside of the received data.

Lagrange Interpolation Formula

If you are having 2 points with coordinates (x1,y1) and (x2,y2), the Lagrange Interpolation will be:

y - y1= (y2- y1)/(x2-x1) * (x-x1)

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Proof of Lagrange Theorem

Consider the nth-degree polynomial provided by the following expression:

F(x) = A0 (x-x1) (x-x2) (x-x3)....(x-xn) + A1 (x-x0) (x-x2) (x-x3)....(x-xn) +........ + An (x-x1) (x-x2) (x-x3)….(x-xn-1)

Now we substitute the values of our observations, xi, to get the values of Ai:

So we put x = x0 and obtain A0 as seen below:

f(x0) = A0 (x0-x1) (x0-x2) (x0-x2).... (x0-xn), all other terms become zero.

As a result, A0 = y0/(x0-x1) (x0-x2) (x0-x3)... (x0-xn)

Likewise, for x1, we would receive

f(x1) = y1 = = A1 (x1-0) (x2-0) (x3-0).... Other terms become 0 as a result of (x1-xn).

As a result, A1 = y1/(x1-x0) (x1-x2) (x1-x3)... (x1-xn)

We may retrieve all of the As values from A2, A3,... in this manner. An

An is equal to yn/(xn-x0) (xn-x2) (xn-x3).... (xn-xn-1)

We get Lagrange's interpolation theorem if we substitute all the values of As in the main function:

F(x) = y0 * (x-x1) (x-x2) (x-x3)....(x-xn) + y1 * (x-x0) (x-x2) (x-x3)

....(x-xn)/ (x1-x0) (x1-x2) (x1-x3)....(x1-xn) +........+ yn (x-x1) (x-x2) (x-x3)....(x-xn-1)/ (xn-x0) (xn-x2) (xn-x3)....(x-xn-1)/ (xn-x2) (xn-x3)... (xn-xn-1)

Lagrange Interpolation Properties

• If G is a finite order m group, then the order of any aG divides the order of G, and am = e.
• If finite group G's order is a prime order, it has no appropriate subgroups.
• A cyclic group is a group of prime order (the order has only two divisors).

Examples of Lagrange Interpolation

Given these three points, we want to interpolate (x) = x2 across the domain 1 <= x<=  3.

x0=1; f(x0)=1;

x1=2; f(x1)=4;

x2=3; f(x2)=9;

L(x) = 1*((x-2)/(1-2))*((x-3)/(1-3)) + 4*((x-1)/(2-1)*(x-3)(2-3)) + 9*((x-1)/(3-1)*(x-2)/(3-2)) = x^2

When to Use Lagrange Interpolation

This formula is used to determine the function's value even when the parameters are not evenly spaced. This formula is used to calculate the value of the independent variable x that corresponds to a given function value. One common application is in image scaling, where one interpolates the next position of a pixel based on the given positions of pixels in an image.

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Benefits of Lagrange Interpolation

When interpolating several data sets on the same data points, Lagrange's form is more efficient. This formula is used to determine the function's value even when the parameters are not evenly spaced. This formula is used to calculate the value of the independent variable x that corresponds to a given function value.

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Conclusion

The Lagrange theorem generalizes well-known mathematical principles such as the idea that a line may be uniquely specified by two points, the graph of a quadratic polynomial by three points, and so on. It is used in the picture enlargement technique to estimate unknown data by attempting to explain the tendency of image data using interpolation polynomials. This assists in picture enlargement. 

The Newton forward and backward interpolation formulae can only be used when the values of x are equidistant. If the values of x are equidistant or not, we use Lagrange's interpolation formula. In this case, the data has been interpolated using Polynomial data, a variable using Wolfram Language. Lagrange interpolating polynomials are often employed in the development of Newton-Cotes formulas. Learn more about Data Analytics topics such as Interpolation with our PGP in Data Analytics. Start your Data career today!

FAQs

1. What do you mean by Lagrange interpolation?

Using the Lagrange Interpolation Formula, one may obtain the Lagrange polynomial. a polynomial that assumes certain values at each given position. It is a polynomial expression of the function f at the nth degree (x). The new data points are located using the interpolation approach inside the bounds of a discrete set of existing data points.

2. What is the purpose of Lagrange interpolation?

The form functions of a cubic element are directly defined by the Lagrange interpolation functions.

3. Where is Lagrange interpolation used?

It is still possible to use this formula to obtain the value of the function even when the parameters are not evenly distributed. Based on a function value, the independent variable x's value is determined by using this formula.

4. What is the Lagrange interpolation polynomial formula?

y - y1= (y2- y1)/(x2-x1) * (x-x1)

5. What is the importance of the Lagrange equation?

The fact that the Euler-Lagrange equation can be used to obtain the equations of motion of a system in any set of coordinates, other than just the usual Cartesian coordinates, is a key feature of the Lagrangian formulation.

6. What is the Lagrange principle?

The formula for the Lagrangian L is L = T V, where T denotes the system's kinetic energy and V is its potential energy. In general, a system's potential energy relies on the coordinates of each of its constituent particles; this is denoted by V = V. (x 1, y 1, z 1, x 2, y 2, z 2, . . . ).