3 research outputs found
"On the engineers' new toolbox" or Analog Circuit Design, using Symbolic Analysis, Computer Algebra, and Elementary Network Transformations
In this paper, by way of three examples - a fourth order low pass active RC
filter, a rudimentary BJT amplifier, and an LC ladder - we show, how the
algebraic capabilities of modern computer algebra systems can, or in the last
example, might be brought to use in the task of designing analog circuits.Comment: V1: documentclass IEEEtran, 7 pages, 6 figures. Re-release of the
printed version, with some minor typographical errors correcte
Time-dependent shortest paths in bounded treewidth graphs
We present a proof that the number of breakpoints in the arrival function
between two terminals in graphs of treewidth is when the
edge arrival functions are piecewise linear. This is an improvement on the
bound of by Foschini, Hershberger, and Suri for graphs
without any bound on treewidth. We provide an algorithm for calculating this
arrival function using star-mesh transformations, a generalization of the
wye-delta-wye transformations
Electrical Reduction, Homotopy Moves, and Defect
We prove the first nontrivial worst-case lower bounds for two closely related
problems. First, degree-1 reductions, series-parallel
reductions, and Y transformations are required in the worst case to
reduce an -vertex plane graph to a single vertex or edge. The lower bound is
achieved by any planar graph with treewidth . Second,
homotopy moves are required in the worst case to reduce a
closed curve in the plane with self-intersection points to a simple closed
curve. For both problems, the best upper bound known is , and the only
lower bound previously known was the trivial .
The first lower bound follows from the second using medial graph techniques
ultimately due to Steinitz, together with more recent arguments of Noble and
Welsh [J. Graph Theory 2000]. The lower bound on homotopy moves follows from an
observation by Haiyashi et al. [J. Knot Theory Ramif. 2012] that the standard
projections of certain torus knots have large defect, a topological invariant
of generic closed curves introduced by Aicardi and Arnold. Finally, we prove
that every closed curve in the plane with crossings has defect
, which implies that better lower bounds for our algorithmic
problems will require different techniques.Comment: 27 pages, 15 figure