# Help with integration

1. Mar 24, 2008

### damjanisa

Hi every body

I've tryed to solve this integration but I can not. Please if any one can help plsease DO HELP.

Integral of { Exp(-x-(t/(a+bx)))dx} from 0 to infinity.

Thanks for any help

2. Mar 24, 2008

### BrendanH

There doesn't seem to be any immediate solution to this problem... are you sure you've written/interpreted it correctly?

Last edited: Mar 24, 2008
3. Mar 25, 2008

### damjanisa

YES I AM SURE
i KNOW IT IS hard to solve it but I hope some one can DO IT

4. Mar 25, 2008

### cristo

Staff Emeritus
Why do you think a solution must exist? Have you tried with a computer algebra package first, to check that the integral does exist?

5. Mar 25, 2008

### Schrodinger's Dog

?

But my maths program fires out.

$$\int e^{[-x-(\frac{t}{a+bx})]}\:dx\rightarrow\int e^{[-x-(\frac{t}{a+bx})]}\:dx$$

As a general solution. Which generally means there isn't one.

Last edited: Mar 25, 2008
6. Mar 25, 2008

### dextercioby

Does this baby $\int_{0}^{\infty} \mbox{exp}\left(-\frac{1}{x}\right) {} \ dx$ exist in $\mathbb{R}$ ? If so, can you compute it ?

7. Mar 27, 2008

### damjanisa

I found this integration in on of published paper in the mobile communication section.

by using matlab: int(exp(-1/x)) = x*exp(-1/x)-Ei(1,1/x), and

int(exp(-1/x),0,inf) , ans = Inf,

I thanks all of you whose trying to help me.

hoever, I hope this will add some knowledge to all of us.

Thans again.

8. Mar 27, 2008

### Schrodinger's Dog

Ah so the Exponential/log integral function turns up again. Problem with that is most maths programs will not give that as a solution. Mine didn't, and it is perfectly capable of churning out the exponential log function as an answer(see here):

See this thread for the logarithmic integral.

http://mathworld.wolfram.com/LogarithmicIntegral.html

Thanks damjanisa that was quite an education.

Last edited: Mar 27, 2008
9. Mar 30, 2008

### damjanisa

Hi, Schrodinger's Dog

However, I tried to undestand what you have said but I can not. I don't know may because I have more than one thing to do these days. I'm sorry.

I understood there is a solution to this integration but I can not know how I do it.
Please if you have more time give me some hints or more explination.

BEST REGARDS DEAR
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10. Mar 30, 2008

### Schrodinger's Dog

Did you check the links, they explain the function. If the answer is infinite the only other solution would be some sort of expansion. Is that what you are looking for?