nyquist function

Nyquist Frequency Response for continuous-time Linear Systems.

nyquist computes the real and imaginary parts of the frequency response of system sys

at given frequencies w

nyquist(sys, w, iu)

Arguments

• sys: LTI system of transfer-function, state-space and zero-pole classes
• w: vector of range of frequencies at the response is computed in rad/sec
• iu: number to specify an input for a MIMO state-space system. If the system has 3 inputs, then iu would be set to 1, set to 2 and then to 3 to obtain the nyquist response from input 1, 2, and 3 to the outputs. For single input systems, iu is always set to 1. iu is not needed/allowed for calls to nyquistplot

Returns

A list is returned by calling nyquist containing: h.real - real part of the frequency response

h.imag - imaginary part of the frequency response

A plot is returned by calling nyquistplot

Details

nyquist Compute the real and imaginary parts of the frequency response of system sys

at given frequencies w. When sys is a transfer function, nyquist

computes the frequency response of the system using the signal package.

nyquistplot plots the frequency response computed by nyquist. For a MIMO state-space system, nyquistplot uses selectsys to obtain the nyquist response for each input-to-output pair and plot them individually. This means that for a 2-input, 2-output system, nyquistplot obtains the response for input 1 to output 1, input 1 to output 2, input 2 to output 1 and input 2 to output 2. nyquistplot uses the subtitle argument to allow a user assign the plot a sub-title

Other possible calls using nyquist and nyquistplot are:

nyquist(sys)

nyquist(sys, w)

nyquist(sys, w = seq(0, 100, length = 10000), iu = 1)

nyquistplot(sys)

nyquistplot(sys, w)

nyquistplot(sys, w, subtitle)

Examples

nyquist(tf(100, c(1,6,100)))
nyquist(ssdata(tf(100, c(1,6,100))))

## Not run:  MIMO plot 
A1 <- rbind(c(0,1), c(-25,-4)); B1 <- rbind(c(1,1), c(0,1))
C1 <- rbind(c(1,0), c(0,1)); D1 <- rbind(c(0,0), c(0,0))
sys1 <- ss(A1,B1,C1,D1)
nyquistplot(sys1)
## Not run:
 Use nyquistplot(selectsys(sys1,1,2)) to obtain the response for a subsystem
 of sys1 for input 1 and output 2 only.

 RESET your plot layout using par(mfrow = c(1,1)
## End(Not run)

See Also

bode