A System object™ is a specialized kind of MATLAB® object that is optimized for iterative processing. Use System objects when you need to run an object multiple times or process data in a loop. When defining your own System object, use the following suggestions to help your code run efficiently.
Define all one-time calculations in the
setupImpl method and cache the results in
a private property. Use the
stepImpl method for repeated calculations.
If properties are accessed more than once in the
stepImpl method, cache those
properties as local variables inside the method. A typical example of multiple property access is a loop. Iterative
calculations using cached local variables run faster than calculations that must access the properties of an object.
When the calculations for the method complete, you can save the local cached results back to the properties of that
object. Copy frequently used tunable properties into private properties. This best practice also applies to the
In this example,
k is accessed multiple times in each loop iteration, but is saved to the object
property only once.
function y = stepImpl(obj,x) k = obj.MyProp; for p=1:100 y = k * x; k = k + 0.1; end obj.MyProp = k; end
Property default values are shared across all instances of an object. Two instances of a class can access the same default value if that property has not been overwritten by either instance.
Do not use character vector comparisons or character vector-based switch statements in the
stepImpl method. Instead, create a method handle in
setupImpl. This handle
points to a method in the same class definition file. Use that handle in a loop in
This example shows how to use method handles and cached local variables in a loop to implement an efficient object.
based on a character vector comparison and assign the method handle to the
Because there is a loop in
stepImpl, assign the
property to a local method handle,
myFun, and then use
myFun inside the loop.
classdef MyClass < matlab.System function setupImpl(obj) if strcmp(obj.Method, 'Method1') obj.pMethodHandle = @myMethod1; else obj.pMethodHandle = @myMethod2; end end function y = stepImpl(obj,x) myFun = obj.pMethodHandle; for p=1:1000 y = myFun(obj,x) end end end function y = myMethod1(x) y = x+1; end function y = myMethod2(x) y = x-1; end end
If the number of System
object inputs does not change, do not implement the
Also do not implement the
getNumInputsImpl method when you explicitly list the inputs
stepImpl method instead of using
varargin. The same caveats
apply to the
methods, if you set the return argument from an object property, that object property must have the
If the variables in a method do not need to retain their values between calls use local scope for those variables in that method.
For properties that do not change, define them in as
Tunable properties have slower access times than
private attribute instead of the
public attribute for a property, whenever possible. Some
public properties have
slower access times than
Avoid using a customized
set methods, whenever
Avoid using character vector comparisons within a customized
set methods, whenever possible. Use
setupImpl for character vector
Specify Boolean values using
false instead of
For best practices for including System objects in code generation, see System Objects in MATLAB Code Generation (MATLAB Coder).
All methods, except static methods, expect the System object handle as the first input argument. You can use any name for your System object handle. In many examples, instead of passing in the object handle, ~ is used to indicate that the object handle is not used in the function. Using ~ instead of an object handle prevents warnings about unused variables.