Understanding the incomplete gamma function

In summary, the conversation discusses the gamma function and its relation to the lower bound incomplete gamma function. The second equation, which involves a constant in the exponent, raises the question of whether it can be used in the evaluation of the lower bound incomplete gamma function. The question remains whether this is a valid approach.
  • #1
badtwistoffate
81
0
I know that the gamma function (from 0 to infinity):
[tex]\int [/tex] e-t tx-1 dt = [tex]\Gamma[/tex](x)

and that the relation exists...

[tex]\int [/tex] e-ut tx-1 dt = 1/ux [tex]\Gamma[/tex](x)

Now for the lower bound incomplete gamma function... I see that from
http://people.math.sfu.ca/~cbm/aands/page_260.htm (equation 6.5.2):

[tex]I[/tex](s,x) = P(a,x) [tex]\Gamma[/tex](x) = [tex]\int [/tex] e-t tx-1 dt (evaluated from 0 to x). Where the far left hand side is the result of the incomplete gamma function (lower bound).

Thus, my question/problem is can we use this relation (second equation) in the evaluation of the lower bound incomplete gamma function.

that:


1/ux [tex]I[/tex](s,x) = 1/ux P(a,x) [tex]\Gamma[/tex](x) = [tex]\int [/tex] e-ut tx-1 d (evaluated from 0 to x)

Since we are just pulling out that factor of 1/u^x anyway. This correct? Can we use that relation this way?
 
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  • #2
badtwistoffate said:
I know that the gamma function (from 0 to infinity):
[tex]\int [/tex] e-t tx-1 dt = [tex]\Gamma[/tex](x)

and that the relation exists...

[tex]\int [/tex] e-ut tx-1 dt = 1/ux [tex]\Gamma[/tex](x)

Now for the lower bound incomplete gamma function... I see that from
http://people.math.sfu.ca/~cbm/aands/page_260.htm (equation 6.5.2):

[tex]I[/tex](s,x) = P(a,x) [tex]\Gamma[/tex](x) = [tex]\int [/tex] e-t tx-1 dt (evaluated from 0 to x). Where the far left hand side is the result of the incomplete gamma function (lower bound).

Thus, my question/problem is can we use this relation (second equation) in the evaluation of the lower bound incomplete gamma function.

that:1/ux [tex]I[/tex](s,x) = 1/ux P(a,x) [tex]\Gamma[/tex](x) = [tex]\int [/tex] e-ut tx-1 d (evaluated from 0 to x)

Since we are just pulling out that factor of 1/u^x anyway. This correct? Can we use that relation this way?

Thus, instead of just a -t in the exponent, there is now a constant with it! So is this legal?
 

FAQ: Understanding the incomplete gamma function

1. What is the incomplete gamma function?

The incomplete gamma function, denoted as Γ(a,x), is a mathematical function used in statistics and applied mathematics to describe the relationship between the gamma distribution and the chi-squared distribution. It is defined as the integral of the gamma probability density function from 0 to x.

2. How is the incomplete gamma function calculated?

The incomplete gamma function can be calculated using various methods, such as numerical integration, series expansion, or recurrence relations. However, the most commonly used method is the continued fraction expansion, which provides a fast and accurate calculation for most values of a and x.

3. What is the significance of the incomplete gamma function?

The incomplete gamma function has various applications in science and engineering, particularly in statistics, probability, and physics. It is used to calculate probabilities and cumulative distribution functions for the gamma and chi-squared distributions, as well as in solving differential equations and series expansions in physics.

4. How does the incomplete gamma function differ from the complete gamma function?

The complete gamma function, denoted as Γ(a), is defined as the integral of the gamma probability density function from 0 to infinity. The incomplete gamma function, on the other hand, has a lower limit of integration at 0 and an upper limit at x. It can be seen as a generalization of the complete gamma function, with the complete gamma function being a special case of the incomplete gamma function when x approaches infinity.

5. Can the incomplete gamma function be extended to complex numbers?

Yes, the incomplete gamma function can be extended to complex numbers, where both a and x are complex. This extension is useful in solving problems involving complex variables in mathematics and physics. The properties and behavior of the incomplete gamma function in the complex plane are still being studied and researched by mathematicians and scientists.

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