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  2. Perturbation theory (quantum mechanics) - Wikipedia

    en.wikipedia.org/wiki/Perturbation_theory...

    For the first-order perturbation, we need solve the perturbed Hamiltonian restricted to the degenerate subspace D, | = | + | , simultaneously for all the degenerate eigenstates, where are first-order corrections to the degenerate energy levels, and "small" is a vector of () orthogonal to D.

  3. RC circuit - Wikipedia

    en.wikipedia.org/wiki/RC_circuit

    A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. It may be driven by a voltage or current source and these will produce different responses. A first order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit.

  4. Method of characteristics - Wikipedia

    en.wikipedia.org/wiki/Method_of_characteristics

    For a first-order PDE, the method of characteristics discovers so called characteristic curves along which the PDE becomes an ODE. [1] [2] Once the ODE is found, it can be solved along the characteristic curves and transformed into a solution for the original PDE.

  5. Hamiltonian (control theory) - Wikipedia

    en.wikipedia.org/wiki/Hamiltonian_(control_theory)

    To derive the first-order conditions for an optimum, assume that the solution has been found and the Lagrangian is maximized. Then any perturbation to x ( t ) {\displaystyle \mathbf {x} (t)} or u ( t ) {\displaystyle \mathbf {u} (t)} must cause the value of the Lagrangian to decline.

  6. Bilinear transform - Wikipedia

    en.wikipedia.org/wiki/Bilinear_transform

    The bilinear transform is a first-order Padé approximant of the natural logarithm function that is an exact mapping of the z-plane to the s-plane.When the Laplace transform is performed on a discrete-time signal (with each element of the discrete-time sequence attached to a correspondingly delayed unit impulse), the result is precisely the Z transform of the discrete-time sequence with the ...

  7. Roll-off - Wikipedia

    en.wikipedia.org/wiki/Roll-off

    First-order RC filter low-pass filter circuit. Roll-off of a first-order low-pass filter is 20 dB/decade (≈6 dB/octave) A simple first-order network such as a RC circuit will have a roll-off of 20 dB/decade. This is a little over 6 dB/octave and is the more usual description given for this roll-off.

  8. Small-signal model - Wikipedia

    en.wikipedia.org/wiki/Small-signal_model

    Many of the electrical components used in simple electric circuits, such as resistors, inductors, and capacitors are linear. [citation needed] Circuits made with these components, called linear circuits, are governed by linear differential equations, and can be solved easily with powerful mathematical frequency domain methods such as the Laplace transform.

  9. First-order partial differential equation - Wikipedia

    en.wikipedia.org/wiki/First-order_partial...

    The general solution to the first order partial differential equation is a solution which contains an arbitrary function. But, the solution to the first order partial differential equations with as many arbitrary constants as the number of independent variables is called the complete integral. The following n-parameter family of solutions