Solving Bernoulli's ODEs
Description
Examples
The general form of Bernoulli's equation is given by:
Bernoulli_ode := diff(y(x),x)+f(x)*y(x)+g(x)*y(x)^a;
Bernoulli_ode≔ⅆⅆxy⁡x+f⁡x⁢y⁡x+g⁡x⁢y⁡xa
where f(x) and g(x) are arbitrary functions, and a is a symbolic power. See Differentialgleichungen, by E. Kamke, p. 19. Basically, the method consists of making a change of variables, leading to a linear equation which can be solved in general manner. The transformation is given by the following:
with⁡DEtools,odeadvisor
odeadvisor
odeadvisor⁡Bernoulli_ode
_Bernoulli
with⁡PDEtools,dchange
dchange
ITR ≔ y⁡x=u⁡t11−a,x=t
ITR≔x=t,y⁡x=u⁡t11−a
and the ODE becomes
new_ode ≔ dchange⁡ITR,Bernoulli_ode,u⁡t,t:
new_ode2 ≔ solve⁡new_ode,ⅆⅆt⁢u⁡t:
op⁡factor⁡combine⁡expand⁡new_ode2,power
ⅆⅆtu⁡t=a−1⁢u⁡taa−1⁢u⁡t−1a−1a⁢g⁡t+u⁡t⁢f⁡t
This ODE can then be solved by dsolve. Afterwards, another change of variables will reintroduce the original variables x and y(x).
The present implementation of dsolve can arrive directly at a general solution for Bernoulli's equation:
ans ≔ dsolve⁡Bernoulli_ode
ans≔y⁡x=ⅇ∫f⁡xⅆxa−1a⁢∫ⅇ∫f⁡xⅆx⁢g⁡xⅇ∫f⁡xⅆx⁢aⅆx+c__1−∫ⅇ∫f⁡xⅆx⁢g⁡xⅇ∫f⁡xⅆx⁢aⅆx1a−1⁢ⅇ∫f⁡xⅆx⁢aa−1
See Also
DEtools
dsolve
quadrature
linear
separable
Bernoulli
exact
homogeneous
homogeneousB
homogeneousC
homogeneousD
homogeneousG
Chini
Riccati
Abel
Abel2A
Abel2C
rational
Clairaut
dAlembert
sym_implicit
patterns
odeadvisor,types
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