“calculus of infinitesimals”, study of continous change
study of rates ath which quantities change.
Example of a straigth line $y=mx+b$, $m=\Delta y / \Delta x$
“Differentialquotient”:
$m = \lim_{x_1 -> x_0} \frac{f(x_1) - f(x_0)}{x_1 - x_0}$
$f'(x) = \frac{d}{dx} f(x) = \lim_{h -> 0} \frac{f(x + h) - f(x)}{h}$
$f''(x) = \frac{d^2}{dx^2} f(x)$
Geometrically, derivative of f at point x=a is slope of tangent line.
Relation between collection of functions and their derivatives.
Ordinary differential equation:
Differential operator
$f'(x)=f(x)^2 * x$
$\frac{dy}{dx} = y^2 * x$
$dy = y^2 * x {dx}$
$\frac{1}{y^2} dy = x {dx}$
$\int \frac{1}{y^2} dy = \int x {dx}$
$-y^{-1} + c_1 = 1/2 x^2 + c_2$
$-(1/y) = 1/2 x^2 + c_2 - c_1$ $(c_2 - c_1 = c)$
$y = \frac{-1}{(1/2 x^2 + c)}$ (y is a function not value, obviously)
$y' + f(x) y = g(x)$ first order, linear, “homogen” if g(x) = 0, else “inhomogen” (“Störfunktion”)
Solve inhomogen eqs:
$y'' + a_1 y' + a_0 * y = g(x)$
$y(x) = y_a(x) + y_p(x)$
General solution of homogen DE $y_a(x)$ (set to 0, solve with characteristic polynom) “Particular” solution of inhomogen DE $y_p(x)$
v=6jypcZkrvLM Mit Störfkt, charakteristisches Polynom, lösen.