You can protect your model design by preventing block parameters from using values outside of a range. For example, if the value of a parameter that represents the angle of an aircraft aileron cannot feasibly exceed a known magnitude, you can specify a design maximum for the parameter in the model.
Fixed-Point Designer™ enables Simulink® to use your range information to calculate best-precision fixed-point scaling for:
Tunable parameters.
Signals, by taking into consideration the range of values that you intend to assign to tunable parameters.
For basic information about block parameters, see Set Block Parameter Values.
When you specify a value range for a block parameter, typically, you can choose to store the information in the block (the model file) or in an external variable or parameter object. Choose a technique based on your modeling goals.
Use other parameters of the same block, if available. For example, you can control the value range of the Gain parameter of a Gain block by using the Parameter minimum and Parameter maximum parameters in the Parameter Attributes tab in the block dialog box. For other blocks, such as n-D Lookup Table and PID Controller, use the Data Types tab.
Use this technique to:
Store the range information in the model file.
Store the range information when you store fixed-point data type information in the block (for example, by setting the Parameter data type parameter of a Gain block to a fixed-point type, including best-precision scaling). This technique more clearly associates the range information with the data type information.
Use parameter objects (for example,
Simulink.Parameter) to set the parameter value. You
can specify the range information in the object, instead of the block,
by using the Min and Max
properties of the object.
Use this technique to:
Specify range information for blocks that cannot store minimum or maximum information, for example, many blocks in the Continuous library.
Specify range information for a single value that you
share between multiple block parameters (see Share and Reuse Block Parameter Values by Creating Variables). Instead of using a numeric MATLAB® variable, use a parameter object so that you
can specify the Min and
Max properties.
Store the range information when you store fixed-point
data type information in a parameter object (by setting the
DataType property to a fixed-point
type instead of auto). This technique
more clearly associates the range information with the data
type information.
If you specify the range information in a parameter object, consider
removing the range information from the block. For example, on the
Parameter Attributes tab of a
Gain block dialog box, set Parameter
minimum and Parameter maximum to
[]. Some tools, such as the Fixed-Point Tool, use
the range information that you specify in the block only if you do not
specify the range information in the parameter object. If you specify
the range information in the parameter object, the tools ignore the
range information that you specify in the block.
For basic information about creating and using data objects, see Data Objects.
Specify a minimum or maximum as an expression that evaluates to a scalar, real number with
double data type. For example, you can specify a minimum
value for the Gain parameter in a Gain block
by setting Parameter minimum:
A literal number such as 98.884.
Implicitly, the data type is double.
A numeric workspace variable (see Share and Reuse Block Parameter Values by Creating Variables)
whose data type is double. Use this technique to
share a minimum or maximum value between multiple data items.
However, you cannot use variables to set the Min or Max properties
of a parameter object.
To leave the minimum or maximum of a block parameter or parameter
object unspecified, use an empty matrix [], which
is the default value.
If the value of a block parameter is a vector or matrix, the range information that you specify applies to each element of the vector or matrix. If the value of any of the elements is outside the specified range, the model generates an error.
If the value of a block parameter is a structure or a field of a structure, specify range
information for the structure fields by creating a
Simulink.Parameter object whose data type is a Simulink.Bus object. Specify the range information
by using the properties of the signal elements in the bus object. For more
information, see Control Field Data Types and Characteristics by Creating Parameter Object.
If the value of a block parameter is complex (i), the range information that you specify applies separately to the real part and to the imaginary part of the complex number. If the value of either part of the number is outside the range, the model generates an error.
Using the Model Data Editor (on the Modeling tab, click
Model Data Editor), you can specify value ranges for
multiple block parameters and variables with a searchable, sortable table. On
the Parameters tab, set the Change
view drop-down list to Design and
specify values in the Min and Max
columns.
For more information about the Model Data Editor, see Configure Data Properties by Using the Model Data Editor.
To protect your design by preventing block parameters from using values outside of a range, you can specify the minimum and maximum information by using other parameters of the same block. If you or your users set the value of the target parameter outside the range that you specify, the model generates an error.
Whether a block allows you to specify a value range for a parameter, consider using a
parameter object (for example, Simulink.Parameter) to set the value
of the target parameter. Use the properties of the object to specify the range
information. This technique helps you to specify range information for a variable
that you use to set multiple block parameter values.
When you use fixed-point data types in your model, you can enable Simulink to choose a best-precision scaling for block parameters and
Simulink.Parameter objects. If you intend to tune such a
parameter by changing its value during simulation or during execution of the
generated code, the fixed-point scaling chosen by Simulink must accommodate the range of values that you expect to assign to the
parameter.
Also, if you expect to change the value of a parameter, signal data types in the model must accommodate the corresponding expanded range of possible signal values. If you use the Fixed-Point Tool to propose and apply fixed-point data types for a model, to allow the tool to accurately autoscale the signals, specify range information for tunable parameters.
To specify range information for tunable parameters, see Calculate Best-Precision Fixed-Point Scaling for Tunable Block Parameters. To learn how the Fixed-Point Tool autoscales signals by taking into account the value ranges of tunable parameters, see Derive Ranges for Simulink.Parameter Objects (Fixed-Point Designer).
doubleWhen a data item (signal or parameter) uses a data type other
than double, before comparison, Simulink casts
the data item and each design limit (minimum or maximum value that
you specify) to the nondouble data type. This technique helps prevent
the generation of unnecessary, misleading errors and warnings.
However, Simulink stores design limits as double before
comparison. If the data type of the data item has higher precision
than double (for example, a fixed-point data type
with a 128-bit word length and a 126-bit fraction length) or greater
range than double, and double cannot
exactly represent the value of a design limit, Simulink can generate
unexpected warnings and errors.
If the nondouble type has higher precision, consider rounding
the design limit to the next number furthest from zero that double can
represent. For example, suppose that a signal generates an error after
you set the maximum value to 98.8847692348509014.
At the command prompt, calculate the next number furthest from zero
that double can represent.
format long
98.8847692348509014 + eps(98.8847692348509014)ans = 98.884769234850921
Use the resulting number, 98.884769234850921,
to replace the maximum value.
If you have Embedded Coder®, Simulink Coder™ can optimize the code that you generate from the model by taking into account the minimum and maximum values that you specify for signals and parameters. This optimization can remove algorithmic code and affect the results of some simulation modes such as SIL or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).