WOLFRAM

RootLocusPlot[lsys,{k,kmin,kmax}]

generates a root locus plot of a linear time-invariant system lsys as the parameter k ranges from kmin to kmax.

Details and Options

Examples

open allclose all

Basic Examples  (2)Summary of the most common use cases

Root locus plot of a transfer-function model:

Out[1]=1

Root loci of a state-space model:

Out[1]=1

Scope  (3)Survey of the scope of standard use cases

The root locus plot for various pole-zero configurations:

Out[1]=1

Root locus plot of a TransferFunctionModel:

Out[1]=1

Root locus plot of a StateSpaceModel:

Out[1]=1

Generalizations & Extensions  (1)Generalized and extended use cases

A root locus plot can be obtained from a transfer-function model or directly from its expression:

Out[2]=2

Options  (21)Common values & functionality for each option

ColorFunction  (1)

Color stable and unstable parts green and red for a continuous-time system:

Out[1]=1

For a discrete-time system:

Out[2]=2

Epilog  (3)

Show lines corresponding to a damping ratio 0.4 on the plane:

Out[1]=1

Show the circle corresponding to the natural frequency 3 radians per time unit:

Out[1]=1

The loci of points with damping 0.4 in the plane for a system with sampling period 1:

Out[1]=1

FeedbackType  (3)

Negative feedback is assumed by default:

Out[2]=2

Positive feedback:

Out[3]=3

Root loci of an open-loop system with positive feedback:

Out[1]=1

A closed-loop system:

Out[1]=1

Method  (1)

The "NDSolve" method can be faster than "GenericSolve":

Out[2]=2

PlotLegends  (4)

Use placeholder legends for root loci:

Out[2]=2

Use a list of legend text:

Out[1]=1

Use LineLegend to add a overall legend label:

Out[1]=1

Place the legend above the plot:

Out[1]=1

PlotTheme  (2)

Use a theme with a frame and grid lines:

Out[1]=1

Change the style of the grid lines:

Out[1]=1

PoleZeroMarkers  (6)

By default, open-loop poles at zero and closed-loop poles at the mean parameter value are shown:

Out[1]=1

Show no markers:

Out[1]=1

Show the closed-loop poles only:

Out[1]=1

Use text or typeset labels:

Out[1]=1

Use graphics primitives as the pole-zero markers:

Out[1]=1

Use any 2D or 3D graphics:

Out[1]=1

RegionFunction  (1)

Show the loci only in the region where the closed-loop system is stable:

Out[1]=1

Applications  (3)Sample problems that can be solved with this function

Explore and determine critical points such as break-away, break-in, and imaginary axis crossings:

Out[1]=1

Plot the roots of a polynomial as a parameter is varied:

Out[1]=1

Analyze the effect of the sensor gain on a system:

Out[2]=2

Properties & Relations  (6)Properties of the function, and connections to other functions

The root-locus consists of points with for negative feedback:

Out[3]=3

And points with for positive feedback:

Out[4]=4

The root locus plot does not depend on the sampling period:

Out[1]=1

For strictly proper systems, the root loci go to infinity with straight-line asymptotes:

For the strictly proper system, the number of poles is greater than the number of zeros:

Out[2]=2

The plot shows four loci going to infinity:

Out[3]=3

The slopes of the asymptotes for a negative feedback system:

Out[4]=4

Find where the asymptotes intercept the real axis:

Out[5]=5

Plot the root loci and the asymptotes:

Out[7]=7

The slopes of the asymptotes for a positive feedback system:

Out[8]=8

Plot the root loci and the asymptotes:

Out[10]=10

The break-away and break-in points on the real axis can be computed from the poles and zeros:

Out[3]=3

Select those points for which kInterval[{0,5}]:

Out[6]=6

Show the points on the root locus plot:

Out[7]=7

With the loci and closed-loop poles removed, it becomes a pole-zero plot of the open-loop system:

Out[1]=1

Compute the poles and zeros:

Out[2]=2

Use ListPlot to show the same pole-zero plot:

Out[3]=3

The complex-valued transfer function is a surface with "peaks" at the poles and "valleys" at the zeros:

Out[3]=3

The root locus plot travels from the "peaks" to the "valleys" along the lines of steepest descent:

Out[7]=7

The Bode magnitude plot is the intersection of the surface and the - plane:

Out[11]=11

Possible Issues  (1)Common pitfalls and unexpected behavior

The root loci may not be symmetric with respect to the real axis (but the roots are):

Out[1]=1
Wolfram Research (2010), RootLocusPlot, Wolfram Language function, https://reference.wolfram.com/language/ref/RootLocusPlot.html (updated 2014).
Wolfram Research (2010), RootLocusPlot, Wolfram Language function, https://reference.wolfram.com/language/ref/RootLocusPlot.html (updated 2014).

Text

Wolfram Research (2010), RootLocusPlot, Wolfram Language function, https://reference.wolfram.com/language/ref/RootLocusPlot.html (updated 2014).

Wolfram Research (2010), RootLocusPlot, Wolfram Language function, https://reference.wolfram.com/language/ref/RootLocusPlot.html (updated 2014).

CMS

Wolfram Language. 2010. "RootLocusPlot." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2014. https://reference.wolfram.com/language/ref/RootLocusPlot.html.

Wolfram Language. 2010. "RootLocusPlot." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2014. https://reference.wolfram.com/language/ref/RootLocusPlot.html.

APA

Wolfram Language. (2010). RootLocusPlot. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/RootLocusPlot.html

Wolfram Language. (2010). RootLocusPlot. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/RootLocusPlot.html

BibTeX

@misc{reference.wolfram_2025_rootlocusplot, author="Wolfram Research", title="{RootLocusPlot}", year="2014", howpublished="\url{https://reference.wolfram.com/language/ref/RootLocusPlot.html}", note=[Accessed: 09-April-2025 ]}

@misc{reference.wolfram_2025_rootlocusplot, author="Wolfram Research", title="{RootLocusPlot}", year="2014", howpublished="\url{https://reference.wolfram.com/language/ref/RootLocusPlot.html}", note=[Accessed: 09-April-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_rootlocusplot, organization={Wolfram Research}, title={RootLocusPlot}, year={2014}, url={https://reference.wolfram.com/language/ref/RootLocusPlot.html}, note=[Accessed: 09-April-2025 ]}

@online{reference.wolfram_2025_rootlocusplot, organization={Wolfram Research}, title={RootLocusPlot}, year={2014}, url={https://reference.wolfram.com/language/ref/RootLocusPlot.html}, note=[Accessed: 09-April-2025 ]}