The Nyquist plot of a transfer function 
is the image curve 
in the complex plane
as 
traverses a Nyquist
contour 
.
The part obtained from 
records the frequency response as the real
frequency 
varies. The full plot also includes the images of the closing arc and of any small
indentations around poles on the imaginary
axis. The Nyquist criterion reads the winding number of this plot about the critical
point 
.
Nyquist Plot
See also
Complex Plane, Frequency Response, Nyquist Contour, Nyquist Criterion, Transfer FunctionExplore with Wolfram|Alpha
References
Nyquist, H. "Regeneration Theory." Bell System Tech. J. 11, 126-147, 1932. https://doi.org/10.1002/j.1538-7305.1932.tb02344.x.Cite this as:
Weisstein, Eric W. "Nyquist Plot." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/NyquistPlot.html