How do I write taylor expansion as exponential function?

In summary, the conversation discusses how to write the Taylor expansion of a function of x, y, z as an exponential function, specifically when not at the origin. The cross terms are also mentioned and explained using mathematical equations and a reference to quantum mechanics.
  • #1
dwellexity
25
0
How do I write taylor expansion of a function of x,y,z (not at origin) as an exponential function?
Please see the attached image. I need help with the cross terms. I don't know how to include them in the exponential function?
 

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  • #2
Well, [itex]f(x+y) = f(x) + y \frac{d}{dx} f + \frac{y^2}{2} \frac{d^2}{dx^2} f + ...[/itex], which can be formally written as:

[itex]f(x+y) = e^{y \frac{\partial}{\partial x}} f(x)[/itex]

or to be more physics-like,

[itex]f(x+y) = e^{\frac{i}{\hbar} y p_x} f(x)[/itex]

This is discussed here:
http://en.wikipedia.org/wiki/Translation_operator_(quantum_mechanics)
 

Related to How do I write taylor expansion as exponential function?

1. What is a Taylor expansion?

A Taylor expansion is a mathematical expression that represents a function as an infinite sum of terms, where each term is a polynomial function of the variable(s) of the original function. It is used to approximate a function by using its derivatives at a single point.

2. How do I write a Taylor expansion as an exponential function?

To write a Taylor expansion as an exponential function, you can use the Maclaurin series, which is a special case of the Taylor series. The Maclaurin series for an exponential function is e^x = 1 + x + (x^2)/2! + (x^3)/3! + ... + (x^n)/n!, where n is the number of terms you want to include in the expansion.

3. What is the purpose of writing a Taylor expansion as an exponential function?

The purpose of writing a Taylor expansion as an exponential function is to approximate a function using simpler functions, such as polynomials and exponential functions. This can be useful in situations where the original function is difficult to work with, but its derivatives can be easily calculated.

4. How do I determine the accuracy of a Taylor expansion?

The accuracy of a Taylor expansion can be determined by comparing the Taylor series with the original function. The more terms you include in the series, the closer the approximation will be to the original function. You can also use mathematical techniques, such as the remainder theorem, to determine the error in the approximation.

5. Are there any limitations to using Taylor expansions?

Yes, there are limitations to using Taylor expansions. One limitation is that the series may not converge for all values of the variable. Additionally, the accuracy of the approximation may decrease as you move further away from the point of expansion. It is important to carefully consider the convergence and accuracy of a Taylor expansion before using it as an approximation for a function.

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