FileName

Name of the function or MEXfile storing the model structure,
specified as a string (without extension) or a function handle for
computing the states and the outputs. If 'FileName' is
a string, then it must point to a MATLAB file, Pcode file, or
MEXfile. For more information about the file variables, see Specifying the Nonlinear GreyBox Model Structure.

Order

Number of outputs, inputs, and states of the model, specified
as one of the following:
Vector [Ny Nu Nx] , specifying the
number of model outputs Ny , inputs Nu ,
and states Nx . Structure with fields'Ny' , 'Nu' ,
and 'Nx' .
For time series, Nu is set to 0 ,
and for static model structures, Nx is set to 0 .

Parameters

Parameters of the model, specified as one of the following: Np by1 structure array, where Np is
the number of parameters. The structure contains the following fields:
Field  Description  Default 
Name  Name of the parameters, specified as a string.  'pi' , where i is an integer
in [1,Np] 
Unit  Unit of the parameters, specified as a string.  '' 
Value  Initial value of the parameters, specified as:  
Minimum  Minimum value of the parameters, specified as a real scalar,
column vector, or matrix of the same size as Value . Minimum >= Value for
all components.
 Inf(size(Value)) 
Maximum  Maximum value of the parameters, specified as a real scalar,
column vector, or matrix of the same size as Value . Value <= Maximum for
all components.
 Inf(size(Value)) 
Fixed  Specifies whether parameters are fixed to their initial values,
specified as a boolean scalar, column vector, or matrix of the same
size as Value .  false(size(Value)) — Implies,
estimate all parameters 
Np by1 vector of real finite initial
values, InParameters .
The data is converted into a structure with default values for
the fields Name , Unit , Minimum , Maximum ,
and Fixed . Value is assigned the value InParameters(i) ,
where i is an integer in [1,Np]
Np by1 cell array containing finite
real scalars, finite real vectors, or finite real twodimensional
matrices of initial values.
A structure is created with default values for the fields Name , Unit , Minimum , Maximum ,
and Fixed .
Use dot notation to access the subfields of the i th
parameter. For example, for idnlgrey model M ,
the i th parameter is accessed through M.Parameters(i) and
its subfield Fixed by M.Parameters(i).Fixed .

InitialStates

Initial states of the model parameters specified as one of the
following: Nx by1 structure array, where Nx is
the number of states. The structure contains the following fields:
Field  Description  Default 
Name  Name of the states, specified as a string.  'xi' , where i is an integer
in [1,Nx] 
Unit  Unit of the states, specified as a string.  '' 
Value  Initial value of the initial states, specified as:  
Minimum  Minimum value of the initial states, specified as a real scalar
or 1byNe vector of the same size as Value .Minimum >= Value for
all components.
 Inf(size(Value)) 
Maximum  Maximum value of the parameters, specified as a real scalar
or 1byNe vector of the same size as Value .Value <= Maximum for
all components.
 Inf(size(Value)) 
Fixed  Specifies whether initial states are fixed to their initial
values, specified as boolean scalar or 1byNe vector
of the same size as Value  true(size(Value)) — Implies,
do not estimate the initial states 
[] .
A structure is created with default values for the fields Name , Unit , Minimum , Maximum ,
and Fixed . Value is assigned the value 0 .
A real finite Nx byNe matrix
(InitStates ). Value of the i th structure
array element is InitStates(i,Ne) , a row vector
with Ne elements. Minimum , Maximum ,
and Fixed will be Inf , Inf and true row
vectors of the same size as InitStates(i,Ne) .
Cell array with finite real vectors of size 1byNe or {} (same
as [] ). A structure is created with default values for the fields Name , Unit , Minimum , Maximum ,
and Fixed .
Use dot notation to access the subfields of the i th
initial state. For example, for idnlgrey model M ,
the i th initial state is accessed through M.InitialStates(i) and
its subfield Fixed by M.InitialStates(i).Fixed .

FileArgument

Contains auxiliary variables passed to the ODE file (function
or MEXfile) specified in FileName , specified as
a cell array. These variables are used as extra inputs for specifying
the state and/or output equations. Default: {} .

SimulationOptions

A structure that specifies the simulation method and related
options, containing the following fields:
Field  Description  Default 
AbsTol  Absolute error tolerance. This scalar applies to all
components of the state vector. Applicable to: Variable
step solvers. Assignable value: A positive real value.  1e6 
FixedStep  Step size used by the solver. Applicable
to: Fixedstep timecontinuous solvers. Assignable
values:  'Auto' — Automatically chooses
the initial step. 
InitialStep  Specifies the initial step at which the ODE solver starts. Applicable to: Variablestep, timecontinuous solvers. Assignable values:  'Auto' — Automatically chooses
the initial step. 
MaxOrder  Specifies the order of the Numerical Differentiation
Formulas (NDF). Applicable to: ode15s. Assignable
values: 1, 2, 3, 4 or 5.  5 
MaxStep  Specifies the largest time step of the ODE solver. Applicable
to: Variablestep, timecontinuous solvers. Assignable
values:  'Auto' — Automatically chooses
the time step. 
MinStep  Specifies the smallest time step of the ODE solver. Applicable to: Variablestep, timecontinuous solvers. Assignable values:  'Auto' — Automatically chooses
the time step. 
RelTol  Relative error tolerance that applies to all components
of the state vector. The estimated error in each integration step
satisfies e(i) <= max(RelTol*abs(x(i)), AbsTol(i)) . Applicable to: Variablestep, timecontinuous solvers. Assignable value: A positive real value.  1e3 (0.1% accuracy). 
Solver  ODE (Ordinary Differential/Difference Equation) solver
for solving state space equations. A. Variablestep
solvers for timecontinuous idnlgrey models: 'ode45' — RungeKutta (4,5)
solver for nonstiff problems.
'ode23' — RungeKutta (2,3)
solver for nonstiff problems.
'ode113' — AdamsBashforthMoulton
solver for nonstiff problems.
'ode15s' — Numerical Differential
Formula solver for stiff problems.
'ode23s' — Modified Rosenbrock
solver for stiff problems.
'ode23t' — Trapezoidal solver
for moderately stiff problems.
'ode23tb' — Implicit RungeKutta
solver for stiff problems.
B. Fixedstep solvers for timecontinuous idnlgrey models: 'ode5' — DormandPrince
solver.
'ode4' — Fourthorder RungeKutta
solver.
'ode3' — BogackiShampine
solver.
'ode2' — Heun or improved
Euler solver.
'ode1' — Euler solver.
C. Fixedstep solvers for timediscrete idnlgrey models: 'FixedStepDiscrete' D.
General: 'Auto' — Automatically chooses
one of the previous solvers.  'Auto' — Automatically chooses
one of the previous solvers. 

Report

Summary report that contains information about the estimation
options and results when the model is estimated using the nlgreyest command.
Use Report to query a model for how it was estimated,
including:
The contents of Report are irrelevant if
the model was created by construction.
Status: 'Created by direct construction or transformation. Not estimated.'
Method: ''
Fit: [1x1 struct]
Parameters: [1x1 struct]
OptionsUsed: []
RandState: []
DataUsed: [1x1 struct]
Termination: [1x1 struct]
Estimate the parameters of the model object.
nlgr = nlgreyest(z, nlgr);
Status: 'Estimated using NLGREYEST'
Method: 'Solver: ode45; Search: lsqnonlin'
Fit: [1x1 struct]
Parameters: [1x1 struct]
OptionsUsed: [1x1 idoptions.nlgreyest]
RandState: []
DataUsed: [1x1 struct]
Termination: [1x1 struct]
Option set for the nlgreyest command:
GradientOptions: [1x1 struct]
EstCovar: 1
Display: 'off'
Regularization: [1x1 struct]
SearchMethod: 'auto'
SearchOption: [1x1 idoptions.search.lsqnonlin]
OutputWeight: []
Advanced: [1x1 struct]
If you use nlgreyest to
estimate the model, the fields of Report contain
information on the estimation data, options, and results.
Report is a readonly property.
For more information on this property and how to use it, see Output Arguments in
the nlgreyest reference page
and Estimation Report.

TimeVariable

Independent variable for the inputs, outputs, and—when
available—internal states, specified as a string.
Default: 't' 
NoiseVariance

Noise variance (covariance matrix) of the model innovations e. Assignable value is an ny byny matrix. Typically set automatically by the estimation algorithm.

Ts

Sample time. Ts is a positive scalar representing
the sampling period. This value is expressed in the unit specified
by the TimeUnit property of the model. For a continuous
time model, Ts is equal to 0 (default).
Changing this property does not discretize or resample the model.
Default: 0 
TimeUnit

String representing the unit of the time variable. This property
specifies the units for the time variable, the sample time Ts ,
and any time delays in the model. Use any of the following values:
'nanoseconds'
'microseconds'
'milliseconds'
'seconds'
'minutes'
'hours'
'days'
'weeks'
'months'
'years'
Changing this property has no effect on other properties, and
therefore changes the overall system behavior. Use chgTimeUnit to convert between time
units without modifying system behavior.
Default: 'seconds' 
InputName

Input channel names. Set InputName to a string
for singleinput model. For a multiinput model, set InputName to
a cell array of strings.
Alternatively, use automatic vector expansion to assign input
names for multiinput models. For example, if sys is
a twoinput model, enter:
sys.InputName = 'controls';
The input names automatically expand to {'controls(1)';'controls(2)'} .
When you estimate a model using an iddata object, data ,
the software automatically sets InputName to data.InputName .
You can use the shorthand notation u to refer
to the InputName property. For example, sys.u is
equivalent to sys.InputName .
Input channel names have several uses, including:
Identifying channels on model display and plots Extracting subsystems of MIMO systems Specifying connection points when interconnecting
models
Default: Empty string '' for all input channels 
InputUnit

Input channel units. Use InputUnit to keep
track of input signal units. For a singleinput model, set InputUnit to
a string. For a multiinput model, set InputUnit to
a cell array of strings. InputUnit has no effect
on system behavior.
Default: Empty string '' for all input channels 
InputGroup

Input channel groups. The InputGroup property
lets you assign the input channels of MIMO systems into groups and
refer to each group by name. Specify input groups as a structure.
In this structure, field names are the group names, and field values
are the input channels belonging to each group. For example:
sys.InputGroup.controls = [1 2];
sys.InputGroup.noise = [3 5];
creates input groups named controls and noise that
include input channels 1, 2 and 3, 5, respectively. You can then extract
the subsystem from the controls inputs to all outputs
using:
Default: Struct with no fields 
OutputName

Output channel names. Set OutputName to a
string for singleoutput model. For a multioutput model, set OutputName to
a cell array of strings.
Alternatively, use automatic vector expansion to assign output
names for multioutput models. For example, if sys is
a twooutput model, enter:
sys.OutputName = 'measurements';
The output names automatically expand to {'measurements(1)';'measurements(2)'} .
When you estimate a model using an iddata object, data ,
the software automatically sets OutputName to data.OutputName .
You can use the shorthand notation y to refer
to the OutputName property. For example, sys.y is
equivalent to sys.OutputName .
Output channel names have several uses, including:
Identifying channels on model display and plots Extracting subsystems of MIMO systems Specifying connection points when interconnecting
models
Default: Empty string '' for all output channels 
OutputUnit

Output channel units. Use OutputUnit to keep
track of output signal units. For a singleoutput model, set OutputUnit to
a string. For a multioutput model, set OutputUnit to
a cell array of strings. OutputUnit has no effect
on system behavior.
Default: Empty string '' for all output channels 
OutputGroup

Output channel groups. The OutputGroup property
lets you assign the output channels of MIMO systems into groups and
refer to each group by name. Specify output groups as a structure.
In this structure, field names are the group names, and field values
are the output channels belonging to each group. For example:
sys.OutputGroup.temperature = [1];
sys.InputGroup.measurement = [3 5];
creates output groups named temperature and measurement that
include output channels 1, and 3, 5, respectively. You can then extract
the subsystem from all inputs to the measurement outputs
using:
Default: Struct with no fields 
Name

System name. Set Name to a string to label
the system.
Default: '' 
Notes

Any text that you want to associate with the system. Set Notes to
a string or a cell array of strings.
Default: {} 
UserData

Any type of data you wish to associate with system. Set UserData to
any MATLAB data type.
Default: [] 