nicholsoptions

Plot options for nicholsplot

Description

Use the nicholsoptions function to create a NicholsOptions object. Use this object to customize the appearance of a Nichols plot created using nicholsplot and override the plot preferences for the MATLAB^® session in which you create the Nichols plot.

The options you specify for a NicholsOptions object correspond to properties of a NicholsPlot chart object.

Creation

Syntax

plotoptions = nicholsoptions

plotoptions = nicholsoptions("cstprefs")

Description

plotoptions = nicholsoptions returns a default set of plot options for use with nicholsplot. You can use these options to customize the Nichols plot appearance using the command line. This syntax is useful when you want to write a script to generate plots that look the same regardless of the preference settings of the MATLAB session in which you run the script.

plotoptions = nicholsoptions("cstprefs") initializes the plot options with the options you selected in the Control System Toolbox™ preferences editor Editor. For more information about the editor, see Specify Toolbox Preferences for Linear Analysis Plots. This syntax is useful when you want to change a few plot options but otherwise use your default preferences. A script that uses this syntax can generate results that look different when run in a session with different preferences.

Properties

Units

FreqUnits — Frequency units

'rad/s' (default) | 'Hz' | 'rpm' | 'auto' | ...

Frequency units, specified as one of the following values:

• 'Hz'

• 'rad/s'

• 'rpm'

• 'kHz'

• 'MHz'

• 'GHz'

• 'rad/nanosecond'

• 'rad/microsecond'

• 'rad/millisecond'

• 'rad/minute'

• 'rad/hour'

• 'rad/day'

• 'rad/week'

• 'rad/month'

• 'rad/year'

• 'cycles/nanosecond'

• 'cycles/microsecond'

• 'cycles/millisecond'

• 'cycles/hour'

• 'cycles/day'

• 'cycles/week'

• 'cycles/month'

• 'cycles/year'

You can also specify 'auto' which uses frequency 'rad/TimeUnit', where TimeUnit is the TimeUnit property of the input system.

This option corresponds to the FrequencyUnit property of the chart object.

MagUnits — Magnitude units

'dB' (default) | 'abs'

Magnitude units, specified as one of the following:

• 'dB' — Decibels

• 'abs' — Absolute value

This option corresponds to the MagnitudeUnit property of the chart object.

PhaseUnits — Phase units

'deg' (default) | 'rad'

Phase units, specified as one of the following:

• 'deg' — Degrees

• 'rad' — Radians

This option corresponds to the PhaseUnit property of the chart object.

Magnitude Lower Limit

MagLowerLimMode — Lower magnitude limit mode

'auto' (default) | 'manual'

Lower magnitude limit mode, specified as either 'auto' or 'manual'.

This option corresponds to the MinimumGainEnabled property of the chart object.

MagLowerLim — Lower magnitude limit value

'-inf' (default) | scalar

Lower magnitude limit value, specified as a scalar.

This option corresponds to the MinimumGainValue property of the chart object.

Phase Wrapping and Matching

PhaseWrapping — Enable phase wrapping

'off' (default) | 'on'

Option to enable phase wrapping, specified as either 'off' or 'on'. When phase wrapping is enabled, the phase shown in the response wraps to remain in the range defined by PhaseWrappingBranch.

When both phase wrapping and phase matching are enabled, the software performs the phase matching followed by the phase wrapping.

This option corresponds to the PhaseWrappingEnabled property of the chart object.

PhaseWrappingBranch — Lower limit of phase-wrapping range

-180 (default) | scalar

Lower limit of phase-wrapping range, specified as a scalar value in degrees. The phase-wrapping range is [B,B+360), where B is equal to PhaseWrappingBranch.

This option corresponds to the PhaseWrappingBranch property of the chart object.

PhaseMatching — Enable phase matching

'off' (default) | 'on'

Option to enable phase matching, specified as either 'off' or 'on'. When phase matching is enabled, the phase response matches the value specified in PhaseMatchingValue at the frequency specified in PhaseMatchingFreq. The remaining phase response shifts to maintain the same phase profile.

This option corresponds to the PhaseMatchingEnabled property of the chart object.

When both phase wrapping and phase matching are enabled, the software performs the phase matching followed by the phase wrapping.

PhaseMatchingFreq — Phase matching frequency

0 (default) | scalar

Phase matching frequency, specified as a scalar.

This option corresponds to the PhaseMatchingFrequency property of the chart object.

PhaseMatchingValue — Phase matching response value

0 (default) | scalar

Phase matching response value, specified as a scalar.

This option corresponds to the PhaseMatchingValue property of the chart object.

Inputs and Outputs

IOGrouping — Grouping of input-output pairs

'none' (default) | 'inputs' | 'outputs' | 'all'

Grouping of input-output (I/O) pairs, specified as one of the following:

• 'none' — Do not group inputs or outputs.

• 'inputs' — Group only inputs.

• 'outputs' — Group only outputs.

• 'all' — Group all input-output pairs.

This option corresponds to the IOGrouping property of the chart object.

InputLabels — Input label style

structure

Input label style, specified as a structure with the following fields:

• FontSize — Font size, specified as a scalar value greater than zero in point units. The default font size depends on the specific operating system and locale. One point equals 1/72 inch.

• FontWeight — Character thickness, specified as 'Normal' or 'bold'. MATLAB uses the FontWeight property to select a font from those available on your system. Not all fonts have a bold weight. Therefore, specifying a bold font weight can still result in the normal font weight.

• FontAngle — Character slant, specified as 'Normal' or 'italic'. Not all fonts have both font styles. Therefore, the italic font might look the same as the normal font.

• Color — Text color, specified as an RGB triplet. The default color is dark grey with the RGB triplet [0.4,0.4,0.4].

• Interpreter — Text interpreter, specified as one of these values:

  • 'tex' — Interpret characters using a subset of TeX markup. This is the default value of Interpreter.

  • 'latex' — Interpret characters using LaTeX markup.

  • 'none' — Display literal characters.

This option corresponds to the InputLabels property of the chart object.

OutputLabels — Output label style

structure

Output label style, specified as a structure with the following fields:

• FontSize — Font size, specified as a scalar value greater than zero in point units. The default font size depends on the specific operating system and locale. One point equals 1/72 inch.

• FontWeight — Character thickness, specified as 'Normal' or 'bold'. MATLAB uses the FontWeight property to select a font from those available on your system. Not all fonts have a bold weight. Therefore, specifying a bold font weight can still result in the normal font weight.

• FontAngle — Character slant, specified as 'Normal' or ''italic'. Not all fonts have both font styles. Therefore, the italic font might look the same as the normal font.

• Color — Text color, specified as an RGB triplet. The default color is dark grey with the RGB triplet [0.4,0.4,0.4].

• Interpreter — Text interpreter, specified as one of these values:

  • 'tex' — Interpret characters using a subset of TeX markup. This is the default value of Interpreter.

  • 'latex' — Interpret characters using LaTeX markup.

  • 'none' — Display literal characters.

This option corresponds to the OutputLabels property of the chart object.

InputVisible — Option to display inputs

{'on'} (default) | {'off'} | cell array

Option to display inputs, specified as {'on'}, {'off'}, or a cell array with multiple elements.

This option corresponds to the InputVisible property of the chart object.

OutputVisible — Option to display outputs

{'on'} (default) | {'off'} | cell array

Option to display outputs, specified as {'on'}, {'off'}, or a cell array with multiple elements.

This option corresponds to the OutputVisible property of the chart object.

Title and Axis Labels

Title — Title text and style

structure

Title text and style, specified as a structure with the following fields:

• String — Label text, specified as a character vector. By default, the plot is titled 'Bode Diagram'.

• FontSize — Font size, specified as a scalar value greater than zero in point units. The default font size depends on the specific operating system and locale. One point equals 1/72 inch.

• FontWeight — Character thickness, specified as 'Normal' or 'bold'. MATLAB uses the FontWeight property to select a font from those available on your system. Not all fonts have a bold weight. Therefore, specifying a bold font weight can still result in the normal font weight.

• FontAngle — Character slant, specified as 'Normal' or 'italic'. Not all fonts have both font styles. Therefore, the italic font might look the same as the normal font.

• Color — Text color, specified as an RGB triplet. The default color is black specified by the RGB triplet [0,0,0].

• Interpreter — Text interpreter, specified as one of these values:

  • 'tex' — Interpret characters using a subset of TeX markup. This is the default value of Interpreter.

  • 'latex' — Interpret characters using LaTeX markup.

  • 'none' — Display literal characters.

This option corresponds to the Title property of the chart object.

XLabel — X-axis label text and style

structure

X-axis label text and style, specified as a structure with the following fields:

• String — Label text, specified as a character vector. By default, the axis is titled based on the frequency units FreqUnits.

• FontSize — Font size, specified as a scalar value greater than zero in point units. The default font size depends on the specific operating system and locale. One point equals 1/72 inch.

• FontWeight — Character thickness, specified as 'Normal' or 'bold'. MATLAB uses the FontWeight property to select a font from those available on your system. Not all fonts have a bold weight. Therefore, specifying a bold font weight can still result in the normal font weight.

• FontAngle — Character slant, specified as 'Normal' or 'italic'. Not all fonts have both font styles. Therefore, the italic font might look the same as the normal font.

• Color — Text color, specified as an RGB triplet. The default color is black specified by the RGB triplet [0,0,0].

• Interpreter — Text interpreter, specified as one of these values:

  • 'tex' — Interpret characters using a subset of TeX markup. This is the default value of Interpreter.

  • 'latex' — Interpret characters using LaTeX markup.

  • 'none' — Display literal characters.

This option corresponds to the XLabel property of the chart object.

YLabel — Y-axis label text and style

structure

Y-axis label text and style, specified as a structure with the following fields:

• String — Label text, specified as a cell array of character vectors. By default, the axis label is a 1x2 cell array with 'Magnitude' and 'Phase'.

• FontSize — Font size, specified as a scalar value greater than zero in point units. The default font size depends on the specific operating system and locale. One point equals 1/72 inch.

• FontWeight — Character thickness, specified as 'Normal' or 'bold'. MATLAB uses the FontWeight property to select a font from those available on your system. Not all fonts have a bold weight. Therefore, specifying a bold font weight can still result in the normal font weight.

• FontAngle — Character slant, specified as 'Normal' or 'italic'. Not all fonts have both font styles. Therefore, the italic font might look the same as the normal font.

• Color — Text color, specified as an RGB triplet. The default color is black specified by the RGB triplet [0,0,0].

• Interpreter — Text interpreter, specified as one of these values:

  • 'tex' — Interpret characters using a subset of TeX markup. This is the default value of Interpreter.

  • 'latex' — Interpret characters using LaTeX markup.

  • 'none' — Display literal characters.

This option corresponds to the YLabel property of the chart object.

TickLabel — Tick label style

structure

Tick label style, specified as a structure with the following fields:

• FontSize — Font size, specified as a scalar value greater than zero in point units. The default font size depends on the specific operating system and locale. One point equals 1/72 inch.

• FontWeight — Character thickness, specified as 'Normal' or 'bold'. MATLAB uses the FontWeight property to select a font from those available on your system. Not all fonts have a bold weight. Therefore, specifying a bold font weight can still result in the normal font weight.

• FontAngle — Character slant, specified as 'Normal' or 'italic'. Not all fonts have both font styles. Therefore, the italic font might look the same as the normal font.

• Color — Text color, specified as an RGB triplet. The default color is black specified by the RGB triplet [0,0,0].

Grid

Grid — Toggle grid display

'off' (default) | 'on'

Toggle grid display on the plot, specified as either 'off' or 'on'.

This option corresponds to the GridVisible property of the chart object.

GridColor — Color of the grid lines

[0.15 0.15 0.15] (default) | RGB triplet

Color of the grid lines, specified as an RGB triplet. The default color is light grey specified by the RGB triplet [0.15 0.15 0.15].

Axis Limits

XLimMode — X-axis limit selection mode

'auto' (default) | 'manual' | cell array

X-axis limit selection mode, specified as one of the following values:

• 'auto' — Enable automatic limit selection, which is based on the total span of the plotted data.

• 'manual' — Manually specify the axis limits. To specify the axis limits, set the XLim option.

This option corresponds to the XLimitsMode property of the chart object.

YLimMode — Y-axis limit selection mode

'auto' (default) | 'manual' | cell array

Selection mode for the y-axis limits, specified as one of these values:

• 'auto' — Enable automatic limit selection, which is based on the total span of the plotted data.

• 'manual' — Manually specify the axis limits. To specify the axis limits, set the YLim option.

This option corresponds to the YLimitsMode property of the chart object.

XLim — X-axis limits

'{[1,10]}' (default) | cell array of two-element vectors of the form [min,max] | cell array

X-axis limits, specified as a cell array of two-element vector of the form [min,max].

This option corresponds to the XLimits property of the chart object.

YLim — Y-axis limits

'{[1,10]}' (default) | cell array of two-element vector of the form [min,max] | cell array

Y-axis limits, specified as a cell array of two-element vector of the form [min,max].

This option corresponds to the YLimits property of the chart object.

Object Functions

nicholsplot

Plot Nichols frequency response of dynamic system

Examples

Customize Nichols Plot

For this example, use the plot handle to change the title, turn on the grid, and set axis limits.

Generate a random state-space model with 5 states and create the Nichols plot with chart object np.

rng("default")
sys = rss(5);
np = nicholsplot(sys);

Change the title, enable the grid, and set axis limits.

np.Title.String = "Nichols Frequency Response";
xlim([-2 4])
ylim([3.3 4.3])
grid on

Alternatively, you can also use the nicholsoptions command to specify the required plot options. First, create an options set based on the toolbox preferences.

plotoptions = nicholsoptions('cstprefs');

Change the desired properties of the options set.

plotoptions.Title.String = 'Nichols Frequency Response';
plotoptions.Grid = 'on';
plotoptions.XLim = {[-2,4]};
plotoptions.YLim = {[3.3,4.3]};
nicholsplot(sys,plotoptions);

Depending on your own toolbox preferences, the plot you obtain might look different from this plot. Only the properties that you set explicitly, in this example Title, Grid, XLim and YLim, override the toolbox preferences.

Custom Nichols Plot Settings Independent of Preferences

For this example, create a Nichols plot that uses 15-point red text for the title. This plot should look the same, regardless of the preferences of the MATLAB session in which it is generated.

First, create a default options set using nicholsoptions.

plotoptions = nicholsoptions;

Next, change the required properties of the options set plotoptions.

plotoptions.Title.FontSize = 15;
plotoptions.Title.Color = [1 0 0];
plotoptions.FreqUnits = 'Hz';
plotoptions.Grid = 'on';

Now, create a Nichols plot using the options set plotoptions.

nicholsplot(tf(1,[1,1]),{0,15},plotoptions);

Because plotoptions begins with a fixed set of options, the plot result is independent of the toolbox preferences of the MATLAB session.

Customized Nichols Plot of Transfer Function

For this example, create a Nichols plot of the following continuous-time SISO dynamic system. Then, turn the grid on and rename the plot.

$$sys(s)=\frac{s^2+0.1s+7.5}{s^4+0.12s^3+9s^2}.$$

Create the transfer function sys.

sys = tf([1 0.1 7.5],[1 0.12 9 0 0]);

Next, create the options set using nicholsoptions and change the required plot properties.

plotoptions = nicholsoptions;
plotoptions.Grid = 'on';
plotoptions.Title.String = 'Nichols Plot of Transfer Function';

Now, create the Nichols plot with the custom option set plotoptions.

nicholsplot(sys,plotoptions)

nicholsplot automatically selects the plot range based on the system dynamics.

Nichols Response of Identified Parametric and Nonparametric Models

For this example, compare the Nichols response of a parametric model, identified from input/output data, to a non-parametric model identified using the same data. Identify parametric and non-parametric models based on the data.

Load the data and create the parametric and non-parametric models using tfest and spa, respectively.

load iddata2 z2;
w = linspace(0,10*pi,128);
sys_np = spa(z2,[],w);
sys_p = tfest(z2,2);

spa and tfest require System Identification Toolbox™ software. The model sys_np is a non-parametric identified model while, sys_p is a parametric identified model.

Create an options set to turn phase matching and the grid on. Then, create a Nichols plot that includes both systems using this options set.

plotoptions = nicholsoptions;  
plotoptions.PhaseMatching = 'on';
plotoptions.Grid = 'on';
plotoptions.XLim = {[-240,0]};
h = nicholsplot(sys_p,'r.-.',sys_np,'b.-.',w,plotoptions);
legend('Parametric Model','Non-Parametric model');

Set Options for Nichols Plot

Create an options set, and set the phase units and grid option.

P = nicholsoptions; 
P.PhaseUnits = 'rad';
P.Grid = 'on';

Use the options set to generate a Nichols plot. Note the phase units and grid in the plot.

h = nicholsplot(tf(1,[1,.2,1,0]),P);

Version History

Introduced in R2008a