7,953 research outputs found
A q-analog of Euler's decomposition formula for the double zeta function
The double zeta function was first studied by Euler in response to a letter
from Goldbach in 1742. One of Euler's results for this function is a
decomposition formula, which expresses the product of two values of the Riemann
zeta function as a finite sum of double zeta values involving binomial
coefficients. In this note, we establish a q-analog of Euler's decomposition
formula. More specifically, we show that Euler's decomposition formula can be
extended to what might be referred to as a ``double q-zeta function'' in such a
way that Euler's formula is recovered in the limit as q tends to 1.Comment: 6 page
Verhulst's logistic curve
We observe that the elementary logistic differential equation dP/dt=(1-P/M)kP
may be solved by first changing the variable to R=(M-P)/P. This reduces the
logistic differential equation to the simple linear differential equation
dR/dt=-kR, which can be solved without using the customary but slightly more
elaborate methods applied to the original logistic DE. The resulting solution
in terms of R can be converted by simple algebra to the familiar sigmoid
expression involving P. A biological argument is given for introducing logistic
growth via the simpler DE for R. It is also shown that the sigmoid P may be
written in terms of the hyperbolic tangent by a simple translation that is also
motivated by a biological argument.Comment: 5 pages AMSLaTeX, 2 figure
- …