splane
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In mathematics and engineering, the splane is the complex plane on which Laplace transforms are graphed. It is a mathematical domain where, instead of viewing processes in the time domain modeled with timebased functions, they are viewed as equations in the frequency domain. It is used as a graphical analysis tool in engineering and physics.
A real function in time is translated into the splane by taking the integral of the function multiplied by from to where s is a complex number with the form .
This transformation from the tdomain into the sdomain is known as a Laplace transform and the function is called the Laplace transform of . One way to understand what this equation is doing is to remember how Fourier analysis works. In Fourier analysis, harmonic sine and cosine waves are multiplied into the signal, and the resultant integration provides indication of a signal present at that frequency (i.e. the signal's energy at a point in the frequency domain). The Laplace transform does the same thing, but more generally. The not only catches frequencies, but also the real effects as well. Laplace transforms therefore cater not only for frequency response, but decay effects as well. For instance, a damped sine wave can be modeled correctly using Laplace transforms.
A function in the splane can be translated back into a function of time using the inverse Laplace transform
where the real number is chosen so the integration path is within the region of convergence of . However rather than use this complicated integral, most functions of interest are translated using tables of Laplace transform pairs, and the Cauchy residue theorem.
Analysing the complex roots of an splane equation and plotting them on an Argand diagram can reveal information about the frequency response and stability of a real time system. This process is called root locus analysis.
See also
External links
 Illustration of a mapping from the splane to the zplane
 Kevin Brown (2015) Laplace Transforms at Math Pages.
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