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≔ⅆⅆxyx+fxyx+gxyxa
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:
withDEtools,odeadvisor
odeadvisor
odeadvisorBernoulli_ode
_Bernoulli
withPDEtools,dchange
dchange
ITR≔x=t,yx=ut11−a
and the ODE becomes
new_ode≔dchangeITR,Bernoulli_ode,ut,t:
new_ode2≔solvenew_ode,diffut,t:
opfactorcombineexpandnew_ode2,power
ⅆⅆtut=−1+agtuta−1+aut−1−1+aa+utft
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≔dsolveBernoulli_ode
ans≔yx=ⅇ∫fxⅆx−1+aa∫ⅇ∫fxⅆxgxⅇ∫fxⅆxaⅆx+c__1−∫ⅇ∫fxⅆxgxⅇ∫fxⅆxaⅆx1−1+aⅇ∫fxⅆxa−1+a
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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