Commit a548e118 authored by Martin Reinecke's avatar Martin Reinecke

draft section on accuracy

parent 61b623c6
......@@ -32,6 +32,27 @@ re-implement the central algorithms (like conversions between pixel index and
angular coordinates), which are nontrivial to do correctly for all corner cases.
Accuracy of the provided functions
The library has been designed with the goal of providing highly accurate
results. However, due to finite numerical resolution of floating point data
types and varying accuracy of the mathematical functions used by the code
(trigonometric functions and square root), the results returned by the library
will exhibit some remaining degree of inaccuracy.
For example, ang2ring() or ang2nest() may return the pixel number of any
adjacent pixel when called with positions very close to any pixel boundary
("very close" meaning roughly 10**-15 radians). Prominent examples for such
locations are the spherical poles, which lie at the corner of four HEALPix
pixels, respectively.
Moreover it must not be assumed that function results for identical arguments
will be identical on different hardware platforms, or on binaries produced by
different compilers or with different compilation flags. Running the same binary
within the same computing environment, however, should always produce identical
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