New York City Councilmember Ritchie Torres proposed legislation Wednesday that would require retail establishments to accept cash and forbid them from only accepting credit and debit cards. Retailers and restaurants that do not take physical currency, Torres says, box the unbanked and underbanked—populations that, disproportionately, tend to be non-white—out of the economy. [ more › ] Gothamist https://ift.tt/2AyOQe2 November 29, 2018 at 12:27AM
Van der Pol’s differential equation is The equation describes a system with nonlinear damping, the degree of damping given by μ. If μ = 0 the system is linear and undamped, but for positive μ the system is nonlinear and damped. We will plot the phase portrait for the solution to Van der Pol’s equation in Python using SciPy’s new ODE solver ivp_solve . The function ivp_solve does not solve second-order systems of equations directly. It solves systems of first-order equations, but a second-order differential equation can be recast as a pair of first-order equations by introducing the first derivative as a new variable. Since y is the derivative of x , the phase portrait is just the plot of ( x , y ). If μ = 0, we have a simple harmonic oscillator and the phase portrait is simply a circle. For larger values of μ the solutions enter limiting cycles, but the cycles are more complicated than just circles. Here’s the Python code that made the plot. from scipy import linspace from ...
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