Gamma Function Complex Argument: Problems in Stat Phys & How to Calculate

In summary, the gamma function is used in many problems in statistical physics and it can be calculated for complex arguments using analytic continuation and the functional equation \Gamma(z+1) = z\Gamma(z). For example, to calculate \Gamma(i), we first compute \Gamma(1+i) and then divide by i to get the approximate value of \Gamma(i).
  • #1
Petar Mali
290
0
[tex]\Gamma(z)=\int^{\infty}_0x^{z-1}e^{-x}dz[/tex]
[tex]z\in\mathhad{C}[/tex]

In which problems in statistical physics we need gamma functions of complex argument?

I don't know how to calculate [tex]\Gamma(i)[/tex] for exaple?
 
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  • #2
Petar Mali said:
[tex]\Gamma(z)=\int^{\infty}_0x^{z-1}e^{-z}dz[/tex]
[tex]z\in\mathhad{C}[/tex]

In which problems in statistical physics we need gamma functions of complex argument?

I don't know how to calculate [tex]\Gamma(i)[/tex] for exaple?
Your formula is wrong (typo) Should be

[tex]\Gamma(z)=\int^{\infty}_0x^{z-1}e^{-x}dx[/tex]
 
  • #3
mathman said:
Your formula is wrong (typo) Should be

[tex]\Gamma(z)=\int^{\infty}_0x^{z-1}e^{-x}dx[/tex]

Yes mistake. I make corrcection!
 
  • #4
Petar Mali said:
Yes mistake. I make corrcection!

Not quite: you still have dz when it should be dx.
 
  • #5
[itex]\Gamma(i)[/itex]

Well, the integral definition converges only if [itex]\Re z > 0[/itex], so in particular it does not converge at [itex]z=i[/itex]. So you need to use analytic continuation. But fortunately that is very easy for the [itex]\Gamma[/itex] function, unlike most other functions. Use the functional equation [itex]\Gamma(z+1) = z\Gamma(z)[/itex]. So to compute [itex]\Gamma(i)[/itex] we can compute [itex]\Gamma(1+i)[/itex] then apply the formula.

You cannot expect a closed-form answer. [itex]\Gamma(1+i) \approx .4980156681-.1549498283i[/itex] so divide by [itex]i[/itex] to get [itex]\Gamma(i) \approx -.1549498283-.4980156681i[/itex].
 

Related to Gamma Function Complex Argument: Problems in Stat Phys & How to Calculate

1. What is the gamma function and why is it important in statistical physics?

The gamma function, denoted by Γ(z), is a special function that extends the concept of factorial to non-integer values. It is important in statistical physics because it is used to calculate the probability of a particle being in a certain energy state, which is crucial in understanding the behavior of systems with a large number of particles.

2. What is the complex argument of the gamma function?

The complex argument of the gamma function refers to the fact that it can be evaluated for complex numbers, not just real numbers. This is useful in statistical physics as it allows for the calculation of probabilities for systems with complex energy levels.

3. What are some common problems encountered when using the gamma function in statistical physics?

One common problem is the divergence of the gamma function at negative integers, which can lead to incorrect calculations if not properly accounted for. Another problem is the numerical instability of the function when dealing with large values, which can result in inaccurate results.

4. How can one calculate the gamma function for complex arguments?

There are various methods for calculating the gamma function for complex arguments, such as using the Lanczos approximation or using numerical integration techniques. It is important to use a reliable and accurate method, as small errors in the calculation can greatly affect the final results.

5. What are some applications of the gamma function in statistical physics?

The gamma function is widely used in statistical physics for calculating partition functions, which are essential in determining the properties and behavior of systems at equilibrium. It is also used in the calculation of thermodynamic quantities such as entropy and internal energy. Additionally, the gamma function plays a crucial role in the study of quantum mechanics and the behavior of particles at the atomic level.

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