NAG CL Interface
s17gac (struve_h0)
1
Purpose
s17gac returns the value of the Struve function of order , .
2
Specification
| double |
s17gac (double x,
NagError *fail) |
|
The function may be called by the names: s17gac, nag_specfun_struve_h0 or nag_struve_h0.
3
Description
s17gac evaluates an approximation to the Struve function of order zero, .
Please consult the
NIST Digital Library of Mathematical Functions for a detailed discussion of the Struve function including special cases, transformations, relations and asymptotic approximations.
The approximation method used by this function is based on Chebyshev expansions.
4
References
MacLeod A J (1996) MISCFUN, a software package to compute uncommon special functions ACM Trans. Math. Software (TOMS) 22(3) 288–301
5
Arguments
-
1:
– double
Input
-
On entry: the argument of the function.
Constraint:
where
is the
machine precision as returned by
X02AJC.
-
2:
– NagError *
Input/Output
-
The NAG error argument (see
Section 7 in the Introduction to the NAG Library CL Interface).
6
Error Indicators and Warnings
- NE_ALLOC_FAIL
-
Dynamic memory allocation failed.
See
Section 3.1.2 in the Introduction to the NAG Library CL Interface for further information.
- NE_INTERNAL_ERROR
-
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact
NAG for assistance.
See
Section 7.5 in the Introduction to the NAG Library CL Interface for further information.
- NE_NO_LICENCE
-
Your licence key may have expired or may not have been installed correctly.
See
Section 8 in the Introduction to the NAG Library CL Interface for further information.
- NE_REAL
-
x is too large and the function returns zero.
7
Accuracy
The Chebyshev coefficients used by this function are internally represented to digits of precision. Calling the number of digits of precision in the floating-point arithmetic being used , then clearly the maximum number of correct digits in the results obtained is limited by .
Apart from this, rounding errors in internal arithmetic may result in a slight loss of accuracy, but it is reasonable to assume that the result is accurate to within a small multiple of the machine precision.
8
Parallelism and Performance
s17gac is not threaded in any implementation.
For , is asymptotically close to the Bessel function which is approximately zero to machine precision.
10
Example
This example reads values of the argument from a file, evaluates the function at each value of and prints the results.
10.1
Program Text
10.2
Program Data
10.3
Program Results