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| ID | Category | Severity | Reproducibility | Date Submitted | Last Update | ||
| 0000010 | [ALGLIB] Spec.functions | major | always | 2009-03-10 21:02 | 2009-07-23 12:42 | ||
| Reporter | SergeyB | View Status | public | ||||
| Assigned To | SergeyB | ||||||
| Priority | normal | Resolution | fixed | ||||
| Status | resolved | Product Version | |||||
| Summary | 0000010: FIXED: modified Besel function returns incorrect results | ||||||
| Description |
From: Kors van der Werf < korsvanderwerf@yahoo.com > Hi, Very nice, ythis ALGLib. I use the VB version for now, and it seems the Modified BesselI funtion for orders of negative half integers do not give proper results, can you have a look? Already order = -0.5 fails, and can be compared to the well known sqrt(2/(PI x)) cosh(x) For x=1 it should be 1.2312, I get 0.293525. Could you ahve a look please. |
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| Programming language | All | ||||||
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(0000006) SergeyB (administrator) 2009-03-11 10:21 |
Confirmed: should be 1.2312, returns 0.2935 |
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(0000007) SergeyB (administrator) 2009-03-11 12:15 edited on: 2009-03-11 14:12 |
Fixed. There was an error in original Cephes code when calculating 1F1(v,2*v,2*x) with v=0. Straightforward formula for 1F1 may return 1.0 or NAN (depending on implementation, 1.0 in Cephes), more elaborate calculations gives us 0.5*(1+exp(2*x)). This error can only happen when v=-0.5, should be OK with other values of v. |
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(0000008) SergeyB (administrator) 2009-03-11 23:36 |
Other negative half-integer values should be fixed also... |
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(0000010) SergeyB (administrator) 2009-04-19 11:07 |
Looks like that this subroutine can't calculate modified Bessel functions of negative orders. It is not a bug - it is a limitation of formula used. I've modified documentation... |
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Issue History |
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| Date Modified | Username | Field | Change |
| 2009-03-10 21:02 | SergeyB | New Issue | |
| 2009-03-10 21:02 | SergeyB | Programming language | => VBA |
| 2009-03-10 21:50 | SergeyB | Status | new => assigned |
| 2009-03-10 21:50 | SergeyB | Assigned To | => SergeyB |
| 2009-03-10 21:54 | SergeyB | Assigned To | SergeyB => |
| 2009-03-10 21:55 | SergeyB | Status | assigned => new |
| 2009-03-11 10:20 | SergeyB | Status | new => assigned |
| 2009-03-11 10:20 | SergeyB | Assigned To | => SergeyB |
| 2009-03-11 10:21 | SergeyB | Note Added: 0000006 | |
| 2009-03-11 10:21 | SergeyB | Status | assigned => confirmed |
| 2009-03-11 10:21 | SergeyB | Reproducibility | have not tried => always |
| 2009-03-11 12:04 | SergeyB | Programming language | VBA => All |
| 2009-03-11 12:15 | SergeyB | Note Added: 0000007 | |
| 2009-03-11 12:15 | SergeyB | Status | confirmed => resolved |
| 2009-03-11 12:15 | SergeyB | Fixed in Version | => Next minor release |
| 2009-03-11 12:15 | SergeyB | Resolution | open => fixed |
| 2009-03-11 12:17 | SergeyB | Note Edited: 0000007 | |
| 2009-03-11 14:12 | SergeyB | Note Edited: 0000007 | |
| 2009-03-11 23:36 | SergeyB | Note Added: 0000008 | |
| 2009-03-11 23:36 | SergeyB | Status | resolved => feedback |
| 2009-03-11 23:36 | SergeyB | Resolution | fixed => reopened |
| 2009-04-19 11:07 | SergeyB | Note Added: 0000010 | |
| 2009-04-19 11:07 | SergeyB | Status | feedback => resolved |
| 2009-04-19 11:07 | SergeyB | Resolution | reopened => fixed |
| 2009-04-20 09:42 | SergeyB | Summary | modified Besel function returns incorrect results => FIXED: modified Besel function returns incorrect results |
| 2009-04-20 09:47 | SergeyB | Target Version | => Upcoming release |
| 2009-07-23 12:42 | SergeyB | Category | => Special functions |
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