Question

Trying to solve Bessel function with C++.
http://www.twiddla.com/738376

Answer 1

you can post your source code at http://ideone.com/ and then post a link to it here.
I think that would be easier to read than at twiddla.

Answer 2

Source Code: http://ideone.com/Wju5T

Answer 3

you erased the formula from twiddla?

Answer 4

yep, let me draw it again

Answer 5

ok - I'm reviewing the code now...

Answer 6

where is it going wrong?

Answer 7

in the BESSEL function, it seems i get an infinite loop. I want the loop to stop when the absolute number of a part of the sum is less than 10^(-12).

Answer 8

it may be fruitful to insert some trace statements in your BESSEL function.
trace out the values of each component being constructed.

Answer 9

you can use std::cout to trace the values out

Answer 10

on a separate note, the function could be made more efficient by not computing \((-1)^{m}\) but instead having an integer that just toggles between 1 and -1, e.g.:

int numerator =1
while (...)
{
sm = ...
numerator = -numerator;
}

Answer 11

I changed \[(-1)^m\] with num and that seems to solve the infinite loop problem. I don't know why. But stills the BESSEL function doesn't work for n=2.

Answer 12

What you should try and do is write some unit tests for each of the methods you have created to ensure they are working as expected.
Also, as I suggested above, tracing out the values while looping in the BESSEL function might help you spot where the problem is.