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The general code generation workflow for the Statistics and Machine Learning Toolbox™ functions that are not the object functions of machine learning models is the
same as the workflow described in MATLAB^{®}
Coder™. For details, see Getting Started with MATLAB Coder (MATLAB Coder). To learn
how to generate code for the object functions of machine learning models, see Introduction to Code Generation.

This example briefly explains the general code generation workflow as summarized in this flow chart:

An *entry-point* function, also known as the *top-level* or *primary* function,
is a function you define for code generation. Because you cannot call any function at the
top level using `codegen`

, you must define an entry-point
function that calls code-generation-enabled functions, and generate C/C++ code for the
entry-point function by using `codegen`

. All functions within the
entry-point function must support code generation.

Add the `%#codegen`

compiler directive (or pragma) to the entry-point
function after the function signature to indicate that you intend to generate code for the
MATLAB algorithm. Adding this directive instructs the MATLAB Code Analyzer to help you diagnose and fix violations that would cause errors
during code generation. See Check Code with the Code Analyzer (MATLAB Coder).

For example, to generate code that estimates the interquartile range of a data set using
`iqr`

, define this
function.

function r = iqrCodeGen(x) %#codegen %IQRCODEGEN Estimate interquartile range % iqrCodeGen returns the interquartile range of the data x, % a single- or double-precision vector. r = iqr(x); end

`varargin`

as an input argument. For details, see Code Generation for Variable Length Argument Lists (MATLAB Coder) and Specify Variable-Size Arguments for Code Generation.To generate C/C++ code, you must have access to a compiler that is configured properly. MATLAB Coder locates and uses a supported, installed compiler. To view and change the default C compiler, enter:

`mex -setup`

`codegen`

After setting up your compiler, generate code for the entry-point function by using
`codegen`

or the MATLAB
Coder app. To learn how to generate code using the MATLAB
Coder app, see Generate MEX Functions by Using the MATLAB Coder App (MATLAB Coder).

To generate code at the command line, use `codegen`

. Because C and C++ are statically typed languages, you must
determine the properties of all variables in the entry-point function at compile time.
Specify the data types and sizes of all inputs of the entry-point function when you call
`codegen`

by using the `-args`

option.

To specify the data type and exact input array size, pass a MATLAB expression that represents the set of values with a certain data type and array size. For example, to specify that the generated code from

`iqrCodeGen.m`

must accept a double-precision numeric column vector with 100 elements, enter:testX = randn(100,1); codegen iqrCodeGen -args {testX} -report

The

`-report`

flag generates a code generation report. See Code Generation Reports (MATLAB Coder).To specify that at least one of the dimensions can have any length, use the

`-args`

option with`coder.typeof`

as follows.The values of-args {coder.typeof(

*example_value*,*size_vector*,*variable_dims*)},`example_value`

, and`size_vector`

specify the properties of the input array that the generated code can accept.`variable_dims`

An input array has the same data type as the example values in

.`example_value`

is the array size of an input array if the corresponding`size_vector`

value is`variable_dims`

`false`

.is the upper bound of the array size if the corresponding`size_vector`

value is`variable_dims`

`true`

.specifies whether each dimension of the array has a variable size or a fixed size. A value of`variable_dims`

`true`

(logical 1) means that the corresponding dimension has a variable size; a value of`false`

(logical 0) means that the corresponding dimension has a fixed size.

Specifying a variable-size input is convenient when you have data with an unknown number of observations at compile time. For example, to specify that the generated code from

`iqrCodeGen.m`

can accept a double-precision numeric column vector of any length, enter:testX = coder.typeof(0,[Inf,1],[1,0]); codegen iqrCodeGen -args {testX} -report

`0`

for thevalue implies that the data type is`example_value`

`double`

because`double`

is the default numeric data type of MATLAB.`[Inf,1]`

for thevalue and`size_vector`

`[1,0]`

for thevalue imply that the size of the first dimension is variable and unbounded, and the size of the second dimension is fixed to be 1.`variable_dims`

To specify a character array, such as supported name-value pair arguments, specify the character array as a constant using

`coder.Constant`

. For example, suppose that`'Name'`

is a valid name-value pair argument for`iqrCodeGen.m`

, and the corresponding value`value`

is numeric. Then enter:codegen iqrCodeGen -args {testX,coder.Constant('Name'),value} -report

For more details, see Generate C Code at the Command Line (MATLAB Coder) and Specify Properties of Entry-Point Function Inputs (MATLAB Coder).

MATLAB Coder can generate code for these types:

MEX (MATLAB Executable) function

Standalone C/C++ code

Standalone C/C++ code compiled to a static library

Standalone C/C++ code compiled to a dynamically linked library

Standalone C/C++ code compiled to an executable

You can specify the build type using the `-config`

option of
`codegen`

. For more details on setting code
generation options, see Configure Build Settings (MATLAB Coder).

By default, `codegen`

generates a MEX function. A MEX function is a
C/C++ program that is executable from MATLAB. You can use a MEX function to accelerate MATLAB algorithms and to test the generated code for functionality and run-time
issues. For details, see MATLAB Algorithm Acceleration (MATLAB Coder) and Why Test MEX Functions in MATLAB? (MATLAB Coder).

You can use the `-report`

flag to produce a code generation report.
This report helps you debug code generation issues and view the generated C/C++ code. For
details, see Code Generation Reports (MATLAB Coder).

Test a MEX function to verify that the generated code provides the same functionality as the original MATLAB code. To perform this test, run the MEX function using the same inputs that you used to run the original MATLAB code, and then compare the results. Running the MEX function in MATLAB before generating standalone code also enables you to detect and fix run-time errors that are much harder to diagnose in the generated standalone code. For more details, see Why Test MEX Functions in MATLAB? (MATLAB Coder).

Pass some data to verify whether `iqr`

,
`iqrCodeGen`

, and `iqrCodeGen_mex`

return the same
interquartile range.

testX = randn(100,1); r = iqr(testX); r_entrypoint = iqrCodeGen(testX); r_mex = iqrCodeGen_mex(testX);

Compare the outputs by using `isequal`

.

isequal(r,r_entrypoint,r_mex)

`isequal`

returns logical 1 (true) if all the inputs are
equal.

You can also verify the MEX function using a test file and `coder.runTest`

. For details, see Testing Code Generated from MATLAB Code (MATLAB Coder).