ODE-28

Logistic carrying

Rearranged logistic.

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GoverningLogistic carrying

Governing equation

K=r N / (r-\\dot N/N)

$N \in \left[1, 400\right]$

where

r: r (1/y)
N: N (—)
dN: dN (1/y)
K: Logistic carrying (—)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

K=r N / (r-\\dot N/N)

$N \in \left[1, 400\right]$

$N = 1$ $K = 4\times 10^{5}$

Along the curve

②

Domain of the variable — blue

N_{\min} = 1,\quad N_{\max} = 400

$N \in \left[1, 400\right]$

$N = 1$ $N = 1$

Along the curve

③

Response curve — green

K=r N / (r-\\dot N/N)

$N \in \left[1, 400\right]$

$N = 1$ $K = 4\times 10^{5}$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}K}{\mathrm{d}N}

$N \in \left[1, 400\right]$

$N = 3.509$ $K^{\prime} = 4\times 10^{5}$

Along the curve

Lecture brief

Historical brief

Exponential decay, the harmonic oscillator, SIR epidemics, Lotka–Volterra and Bessel are the first solvable ODEs of nature and populations. The lab is rate, period and phase portrait in closed form. This sheet (ODE-28 — Logistic carrying) is the form associated with Logistic carrying. Working symbols: $r$ , $N$ , $dN$ $\rightarrow$ $K$ . Rearranged logistic. Pedagogical SI sheet with a live model and a swept parameter.

Purpose

Purpose: compute

K

from

r

N

dN

in Differential equations via

K=r N / (r-\\dot N/N)

Rearranged logistic. Use it when a real differential equations question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

r = 0.400\,\mathrm{1/y}

N = 80.000\,\mathrm{—}

dN = 8.000\,\mathrm{1/y}

, the governing relation

K=r N / (r-\\dot N/N)

yields

K = 106.667\,\mathrm{—}

. One governing identity, SI units, a single sweep on the sheet. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

r r0.4 1/yN N80 —dN dN8 1/y

Outputs

Logistic carrying K106.667 —

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Narration of this film

One governing identity, SI units, a single sweep on the sheet.

Rearranged logistic. Pedagogical SI sheet with a live model and a swept parameter.

Reading speed

Watch on YouTube