Bessel function accuracy

[George Chan]

From a side-by-side comparison with results generated by both Maple and MatLab, I realized that although the output of the VI "evaluation of Bessel J function" is a double-precision array, the accuracy is only up to single precision. Is there any simple way to increase the accuracy to double precision?

[KileenC]

Hi George,

Since the output of the VI is already in double precision, the VI should already contain the correct number of digits of precision. It's possible, however, that the numeric indicator is not set to be displayed with all the digits. Right-click on the numeric indicator that is being used to display the output of the Bessel VI and select Properties. Then, choose the Format and Precision tab. In this panel, you can now increase the number of digits of precision to be displayed. Hopefully by changing this property you are able to view the entire output of the Bessel function to the proper accuracy you desire.

Best of luck with your application!

Kileen C.
Applications Engineer
National Instruments

[George Chan]

May be I should give more detailed description about the problem. When I evaluate J0(0) (Zero-order Bessel function at x=0), I get 1.0000000028314100 instead of the theoretical value 1.000000000000000000...... The same applies to other values of x and, in general, the output is only valid up to single precision.

I use Labview 6.1 on WinXP system.

[KileenC]

Hi George,

I just tested out the Bessel Function Jv(x) evaluated at J0(0) and you are absolutely right! In LabVIEW 6.1, it does seem that the function is only accurate up to a single precision.

The Bessel Function Jv(x) VI has been corrected in LabVIEW 7. The function returns 1.0000000000000000 as expected. I would suggest upgrading to LabVIEW 7. If you do not have a newer copy of LabVIEW and would need to purchase an upgrade, talk to the Customer Service Representative (CSR) for your area or contact any CSR at (888)280-7645 regarding this issue and they might be able to help you out.

I have attached screenshots of the output of the Beseel Function Jv(x).vi for both LabVIEW 6.1 and 7.0 for your interest.

Thanks again.


Kileen C.
Applications Engineer
National Instruments