Math Question?

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SeanBam . Aug 13 2014 17:48. Posts 953

My cousin needs help with this equation and I do not know anything in this area.

I need the mean of [alpha]*exp(-[beta] *x ), since the standard equation for an exponential is [lambda]*e(-[lambda]*x) and the mean of that is [lambda]**(-1), I can then state that the mean of my equation is [alpha]/[beta] * [beta] ** (-1) which is alpha ... right? RIGHT??

edit: [alpha]/[beta**2] .... which doesn't make sense in light of my data

I know some of you guys are really smart, and not many people have tried to help her with this.

0 votes

nixxxbg Bulgaria. Aug 13 2014 19:45. Posts 436

Your questions does not make much sense.

In your example, you have a random variable X with an exponential distribution. The probability density function (pdf) of the exponential distribution with parameter [lambda] is p(x ; [lambda]) := [lambda]*e(-[lambda]*x) for x >= 0. The expected value (mean) of an exponentially distributed random variable is 1/[lambda].

Now, your question mentions a function p(x; [alpha], [beta]) := [alpha]*exp(-[beta] *x ), which is not clearly a pdf. For example, it needs to integrate to 1 so you need to know something else about the parameters [alpha] and [beta]. I am going to take a guess and say that you are interested in a Gamma distribution, whose mean can be found here:

http://en.wikipedia.org/wiki/Gamma_distribution

Last edit: 13/08/2014 19:47

Almebeast Sweden. Aug 14 2014 03:34. Posts 797

Very good post by nixxxbg, I agree.

After all is said and done, more is said than done.