ODE-24

Separable exp

y'=ay.

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GoverningSeparable exp

Governing equation

y=y_0 e^{at}

$t \in \left[0, 6\right]$

where

y0: y0 (—)
a: a (—)
t: t (—)
y: Separable exp (—)

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

y=y_0 e^{at}

$t \in \left[0, 6\right]$

$t = 0$ $y = 2$

Along the curve

②

Domain of the variable — blue

t_{\min} = 0,\quad t_{\max} = 6

$t \in \left[0, 6\right]$

$t = 0$ $t = 0$

Along the curve

③

Response curve — green

y=y_0 e^{at}

$t \in \left[0, 6\right]$

$t = 0$ $y = 2$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}y}{\mathrm{d}t}

$t \in \left[0, 6\right]$

$t = 0.038$ $y^{\prime} = 0.607$

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-24 — Separable exp) is the form associated with Separable exp. Working symbols: $y0$ , $a$ , $t$ $\rightarrow$ $y$ . y'=ay. Pedagogical SI sheet with a live model and a swept parameter.

Purpose

Purpose: compute

y

from

y0

a

t

in Differential equations via

y=y_0 e^{at}

y'=ay. 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

y0 = 2.000\,\mathrm{—}

a = 0.300\,\mathrm{—}

t = 1.000\,\mathrm{—}

, the governing relation

y=y_0 e^{at}

yields

y = 2.700\,\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

y0 y02 —a a0.3 —t t1 —

Outputs

Separable exp y2.700 —

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Narration of this film

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

y'=ay. Pedagogical SI sheet with a live model and a swept parameter.

Reading speed

Watch on YouTube