11,391 research outputs found
On Kahan's Rules for Determining Branch Cuts
In computer algebra there are different ways of approaching the mathematical
concept of functions, one of which is by defining them as solutions of
differential equations. We compare different such approaches and discuss the
occurring problems. The main focus is on the question of determining possible
branch cuts. We explore the extent to which the treatment of branch cuts can be
rendered (more) algorithmic, by adapting Kahan's rules to the differential
equation setting.Comment: SYNASC 2011. 13th International Symposium on Symbolic and Numeric
Algorithms for Scientific Computing. (2011
Program Verification in the presence of complex numbers, functions with branch cuts etc
In considering the reliability of numerical programs, it is normal to "limit
our study to the semantics dealing with numerical precision" (Martel, 2005). On
the other hand, there is a great deal of work on the reliability of programs
that essentially ignores the numerics. The thesis of this paper is that there
is a class of problems that fall between these two, which could be described as
"does the low-level arithmetic implement the high-level mathematics". Many of
these problems arise because mathematics, particularly the mathematics of the
complex numbers, is more difficult than expected: for example the complex
function log is not continuous, writing down a program to compute an inverse
function is more complicated than just solving an equation, and many algebraic
simplification rules are not universally valid.
The good news is that these problems are theoretically capable of being
solved, and are practically close to being solved, but not yet solved, in
several real-world examples. However, there is still a long way to go before
implementations match the theoretical possibilities
Computing the Lambert W function in arbitrary-precision complex interval arithmetic
We describe an algorithm to evaluate all the complex branches of the Lambert
W function with rigorous error bounds in interval arithmetic, which has been
implemented in the Arb library. The classic 1996 paper on the Lambert W
function by Corless et al. provides a thorough but partly heuristic numerical
analysis which needs to be complemented with some explicit inequalities and
practical observations about managing precision and branch cuts.Comment: 16 pages, 4 figure
Massive Loop Amplitudes from Unitarity
We show, for previously uncalculated examples containing a uniform mass in
the loop, that it is possible to obtain complete massive one-loop gauge theory
amplitudes solely from unitarity and known ultraviolet or infrared mass
singularities. In particular, we calculate four-gluon scattering via massive
quark loops in QCD. The contribution of a heavy quark to five-gluon scattering
with identical helicities is also presented.Comment: Minor modifications, 27 pages including two figure
Truth Table Invariant Cylindrical Algebraic Decomposition by Regular Chains
A new algorithm to compute cylindrical algebraic decompositions (CADs) is
presented, building on two recent advances. Firstly, the output is truth table
invariant (a TTICAD) meaning given formulae have constant truth value on each
cell of the decomposition. Secondly, the computation uses regular chains theory
to first build a cylindrical decomposition of complex space (CCD) incrementally
by polynomial. Significant modification of the regular chains technology was
used to achieve the more sophisticated invariance criteria. Experimental
results on an implementation in the RegularChains Library for Maple verify that
combining these advances gives an algorithm superior to its individual
components and competitive with the state of the art
Difficulties in Complex Multiplication and Exponentiation
During my study of the iteration of functions of the form
, where z,c \in \mathbbC, and is a rational
non-integer larger than 2 (\cite{s1}), I encountered a fundamental difficulty
in the exponentiation of a complex number. This paper will explore this
difficulty and the problems encountered in trying to resolve it using a Riemann
surface which is the direct generalization of the polar form of the complex
plane. This paper will also answer two questions raised by Robert Corless in
his \emph{E.C.C.A.D.} presentation \cite{co}: "Can a Riemann surface variable
be coded? What will the operations be on it?" Unfortunately, the addition
operation will be incompatible with the Riemann surface structure.Comment: 17 pages, 9 figures (.ps format
Improving the Representation and Conversion of Mathematical Formulae by Considering their Textual Context
Mathematical formulae represent complex semantic information in a concise
form. Especially in Science, Technology, Engineering, and Mathematics,
mathematical formulae are crucial to communicate information, e.g., in
scientific papers, and to perform computations using computer algebra systems.
Enabling computers to access the information encoded in mathematical formulae
requires machine-readable formats that can represent both the presentation and
content, i.e., the semantics, of formulae. Exchanging such information between
systems additionally requires conversion methods for mathematical
representation formats. We analyze how the semantic enrichment of formulae
improves the format conversion process and show that considering the textual
context of formulae reduces the error rate of such conversions. Our main
contributions are: (1) providing an openly available benchmark dataset for the
mathematical format conversion task consisting of a newly created test
collection, an extensive, manually curated gold standard and task-specific
evaluation metrics; (2) performing a quantitative evaluation of
state-of-the-art tools for mathematical format conversions; (3) presenting a
new approach that considers the textual context of formulae to reduce the error
rate for mathematical format conversions. Our benchmark dataset facilitates
future research on mathematical format conversions as well as research on many
problems in mathematical information retrieval. Because we annotated and linked
all components of formulae, e.g., identifiers, operators and other entities, to
Wikidata entries, the gold standard can, for instance, be used to train methods
for formula concept discovery and recognition. Such methods can then be applied
to improve mathematical information retrieval systems, e.g., for semantic
formula search, recommendation of mathematical content, or detection of
mathematical plagiarism.Comment: 10 pages, 4 figure
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