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In the separation of variables, these functions are given by solutions to = Hence, the spectral theorem ensures that the separation of variables will (when it is possible) find all the solutions. For many differential operators, such as d 2 d x 2 {\displaystyle {\frac {d^{2}}{dx^{2}}}} , we can show that they are self-adjoint by integration by ...
Laplace's equation on is an example of a partial differential equation that admits solutions through -separation of variables; in the three-dimensional case this uses 6-sphere coordinates. (This should not be confused with the case of a separable ODE, which refers to a somewhat different class of problems that can be broken into a pair of ...
Self-similar solutions appear whenever the problem lacks a characteristic length or time scale (for example, the Blasius boundary layer of an infinite plate, but not of a finite-length plate). These include, for example, the Blasius boundary layer or the Sedov–Taylor shell .
An example of a nonlinear delay differential equation; applications in number theory, distribution of primes, and control theory [5] [6] [7] Chrystal's equation: 1 + + + = Generalization of Clairaut's equation with a singular solution [8] Clairaut's equation: 1
The second-order autonomous equation = (, ′) is more difficult, but it can be solved [2] by introducing the new variable = and expressing the second derivative of via the chain rule as = = = so that the original equation becomes = (,) which is a first order equation containing no reference to the independent variable .
This equation attracted a lot of attention in the 1970s due to the presence of soliton solutions, [3] and is an example of an integrable PDE. Among well-known integrable PDEs, the sine-Gordon equation is the only relativistic system due to its Lorentz invariance .
The earliest solution, however, was offered by Gottfried Leibniz, who published his result in the same year and whose method is the one still used today. [5] Bernoulli equations are special because they are nonlinear differential equations with known exact solutions.
An ODE problem can be expanded with the auxiliary variables which make the power series method trivial for an equivalent, larger system. Expanding the ODE problem with auxiliary variables produces the same coefficients (since the power series for a function is unique) at the cost of also calculating the coefficients of auxiliary equations.