matlabFunctionBlock

Convert symbolic expression to MATLAB function block

Syntax

matlabFunctionBlock(block,f)

matlabFunctionBlock(block,f1,...,fN)

matlabFunctionBlock(___,Name,Value)

Description

matlabFunctionBlock(block,f) converts f to a MATLAB^® function block that you can use in Simulink^® models. Here, f can be a symbolic expression, function, or a vector of symbolic expressions or functions.

block specifies the name of the block that you create or modify.

matlabFunctionBlock(block,f1,...,fN) converts symbolic expressions or functions f1,...,fN to a MATLAB function block with N outputs. Each element of f1,...,fN can be a symbolic expression, function, or a vector of symbolic expressions or functions.

matlabFunctionBlock(___,Name,Value) converts a symbolic expression, function, or a vector of symbolic expressions or functions to a MATLAB function block using additional options specified by one or more name-value arguments with any of the input argument combinations in the previous syntaxes.

Examples

Convert Symbolic Expression to MATLAB Function Block

Create a new model and convert a symbolic expression to a MATLAB function block. Include comments in the block by specifying the Comments option.

Create a new model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic expression.

syms x y z
f = x^2 + y^2 + z^2;

Use matlabFunctionBlock to create the block my_block containing the symbolic expression. matlabFunctionBlock overwrites existing blocks.

matlabFunctionBlock('my_system/my_block',f)

Double-click the generated block to open and edit the function defining the block.

function f = my_block(x,y,z)
%#codegen

%    This function was generated by the Symbolic Math Toolbox version 7.3.
%    01-Jan-2017 00:00:00

f = x.^2+y.^2+z.^2;

Include the comment Version 1.1 in the block.

matlabFunctionBlock('my_system/my_block',f,'Comments','Version: 1.1')

function f = my_block(x,y,z)
...
%Version: 1.1
f = x.^2+y.^2+z.^2;

Save and close my_system.

save_system('my_system')
close_system('my_system')

Convert Symbolic Function to MATLAB Function Block

Create a new model and convert a symbolic function to a MATLAB function block.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic function.

syms x y z
f(x,y,z) = x^2 + y^2 + z^2;

Convert f to a MATLAB function block. Double-click the block to see the function.

matlabFunctionBlock('my_system/my_block',f)

function f = my_block(x,y,z)
%#codegen
f = x.^2+y.^2+z.^2;

Create Blocks with Multiple Outputs

Convert several symbolic expressions to a MATLAB function block with multiple output ports.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create three symbolic expressions.

syms x y z
f = x^2;
g = y^2;
h = z^2;

Convert them to a MATLAB function block. matlabFunctionBlock creates a block with three output ports. Double-click the block to see the function.

matlabFunctionBlock('my_system/my_block',f,g,h)

function [f,g,h] = my_block(x,y,z)
%#codegen
f = x.^2;
if nargout > 1
    g = y.^2;
end
if nargout > 2
    h = z.^2;
end

Specify Function Name for Generated Function

Specify the name of the function defining the generated MATLAB function block.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic expression.

syms x y z
f = x^2 + y^2 + z^2;

Generate a block and set the function name to my_function. Double-click the block to see the function.

matlabFunctionBlock('my_system/my_block',f,...
                    'FunctionName','my_function')

function f = my_function(x,y,z)
%#codegen
f = x.^2+y.^2+z.^2;

Disable Code Optimization

When you convert a symbolic expression to a MATLAB function block, matlabFunctionBlock optimizes the code by default. This approach can help simplify and speed up further computations that use the file. Nevertheless, generating the optimized code from some symbolic expressions and functions can be very time-consuming. Use Optimize to disable code optimization.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic expression.

syms x
r = x^2*(x^2 + 1);

Use matlabFunctionBlock to create the block my_block containing the symbolic expression. Double-click the block to see the function defining the block. By default, matlabFunctionBlock creates a file containing the optimized code.

matlabFunctionBlock('my_system/my_block',r)

function r = my_block(x)
%#codegen
t2 = x.^2;
r = t2.*(t2+1.0);

Disable the code optimization by setting the value of Optimize to false.

matlabFunctionBlock('my_system/my_block',r,...
                    'Optimize',false)

function r = my_block(x)
%#codegen
r = x.^2.*(x.^2+1.0);

Specify Input Ports for Generated Block

Specify the order of the input variables that form the input ports in a generated block.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic expression.

syms x y z
f = x^2 + y^2 + z^2;

Convert the expression to a MATLAB function block. By default, matlabFunctionBlock uses alphabetical order of input arguments when converting symbolic expressions.

matlabFunctionBlock('my_system/my_block',f)

function f = my_block(x,y,z)
%#codegen
f = x.^2+y.^2+z.^2;

Use the Vars argument to specify the order of the input ports.

matlabFunctionBlock('my_system/my_block',f,...
                    'Vars',[y z x])

function f = my_block(y,z,x)
%#codegen
f = x.^2+y.^2+z.^2;

Specify Input Ports for Automatically Generated Elements

Specify the input variables explicitly for automatically generated elements.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic variable u and a 3-by-1 vector of symbolic variables x. The following command also automatically generates the symbolic variables x1, x2, and x3 in the MATLAB workspace.

syms u
syms x [3 1]
whos

  Name      Size            Bytes  Class    Attributes

  u         1x1                 8  sym                
  x         3x1                 8  sym                
  x1        1x1                 8  sym                
  x2        1x1                 8  sym                
  x3        1x1                 8  sym                

Create a symbolic expression that uses the symbolic variables u and x.

A = [0 1 0; 0 0 1; -1 -1 -2];
b = [0; 0; 3];
xdot = A*x+b*u

xdot =
 
                  x2
                  x3
3*u - x1 - x2 - 2*x3

Convert the xdot expression to a MATLAB function block. Because the elements of xdot contain the variable u and the automatically generated variables x1, x2, and x3, specify the Vars argument in terms of these variables explicitly instead of using u and x.

matlabFunctionBlock('my_system/my_block',xdot,'Vars',{u,x1,x2,x3})

function xdot = my_block(u,x1,x2,x3)
%#codegen
xdot = [x2;x3;u.*3.0-x1-x2-x3.*2.0];

Specify Output Ports

When generating a block, rename the output variables and the corresponding ports.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic expression.

syms x y z
f = x^2 + y^2 + z^2;

Convert the expression to a MATLAB function block and specify the names of the output variables and ports. Double-click the block to see the function defining the block.

matlabFunctionBlock('my_system/my_block',f,f + 1,f + 2,...
                    'Outputs',{'name1','name2','name3'})

function [name1,name2,name3] = my_block(x,y,z)
%#codegen
t2 = x.^2;
t3 = y.^2;
t4 = z.^2;
name1 = t2+t3+t4;
if nargout > 1
    name2 = t2+t3+t4+1.0;
end
if nargout > 2
    name3 = t2+t3+t4+2.0;
end

Specify Function Name, Input and Output Ports

Call matlabFunctionBlock using several name-value pair arguments simultaneously.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic expression.

syms x y z
f = x^2 + y^2 + z^2;

Call matlabFunctionBlock using the name-value pair arguments to specify the function name, the order of the input ports, and the names of the output ports. Double-click the block to see the function defining the block.

matlabFunctionBlock('my_system/my_block',f,f + 1,f + 2,...
                    'FunctionName','my_function','Vars',[y z x],...
                    'Outputs',{'name1','name2','name3'})

function [name1,name2,name3] = my_function(y,z,x)
%#codegen
t2 = x.^2;
t3 = y.^2;
t4 = z.^2;
name1 = t2+t3+t4;
if nargout > 1
    name2 = t2+t3+t4+1.0;
end
if nargout > 2
    name3 = t2+t3+t4+2.0;
end

Specify Complex Input

Specify a complex input in the generated MATLAB function block.

Create a new empty model and open it.

new_system('my_system')
open_system('my_system')

Create a symbolic function that finds the square root of an input.

syms x
f = sqrt(x);

Convert f to a MATLAB function block.

matlabFunctionBlock('my_system/my_block',f,'FunctionName','sqrt_block')

Because the square root function generates a complex result when the input x is negative, you need to manually specify a complex input in the generated block. Otherwise, you can encounter an error when running the function block with a negative input.

Double-click the block to see the function defining the block. Add the line x = complex(x); to specify a complex input. Starting in R2023a, matlabFunctionBlock provides this line and you can uncomment it. The generated function block now accepts a complex input and returns a complex output.

function f = sqrt_block(x)
%#codegen
x = complex(x);  % required to enforce complex operations on x
f = sqrt(x);
end

As an alternative, you can also insert the Complex to Real-Imag (Simulink) and Real-Imag to Complex (Simulink) blocks from the Simulink > Math Operations library. Add these blocks to convert the input signal that goes into x to a complex signal.

Input Arguments

block — Block to create or modify

character vector

Block to create or modify, specified as a character vector.

f — Symbolic input to be converted to MATLAB function block

symbolic expression | symbolic function | symbolic vector | symbolic matrix

Symbolic input to be converted to a MATLAB function block, specified as a symbolic expression, function, vector, or matrix.

f1,...,fN — Symbolic input to be converted to MATLAB function block with N outputs

several symbolic expressions | several symbolic functions | several symbolic vectors | several symbolic matrices

Symbolic input to be converted to a MATLAB function block with N outputs, specified as several symbolic expressions, functions, vectors, or matrices, separated by commas.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: matlabFunctionBlock('my_system/my_block',f,'FunctionName','myfun')

Comments — Comments to include in file header

character vector | cell array of character vectors | string vector

Comments to include in the file header, specified as a character vector, cell array of character vectors, or string vector.

FunctionName — Name of function

coincides with the input argument block (default) | character vector

Name of the function, specified as a character vector. By default, matlabFunction(block,…) uses block as the function name.

See Specify Function Name for Generated Function.

Optimize — Flag for code optimization

true (default) | false

Flag for code optimization, specified as true or false.

When writing to a file, matlabFunctionBlock optimizes the code using intermediate variables named t0, t1, ....

See Disable Code Optimization.

Vars — Order of input variables and corresponding input ports of generated block

character vector | vector of symbolic variables | one-dimensional cell array of character vectors | one-dimensional cell array of symbolic variables | one-dimensional cell array of vectors of symbolic variables

Order of input variables and corresponding input ports of the generated block, specified as a character vector, a vector of symbolic variables, or a one-dimensional cell array of character vectors, symbolic variables, or vectors of symbolic variables.

The number of specified input ports must equal or exceed the number of free variables in f. Do not use the same names for the input ports specified by Vars and the output ports specified by Outputs.

By default, when you convert symbolic expressions, the order is alphabetical. When you convert symbolic functions, their input arguments appear in front of other variables, and all other variables are sorted alphabetically.

See Specify Input Ports for Generated Block.

Outputs — Names of output ports

out followed by output port numbers (default) | one-dimensional cell array of character vectors

Names of output ports, specified as a one-dimensional cell array of character vectors. If you do not specify the output port names, matlabFunctionBlock uses names that consist of the word out followed by output port numbers, for example, out3.

Do not use the same names for the input ports specified by Vars and the output ports specified by Outputs. See Specify Output Ports.

Limitations

• Some symbolic functions that have no corresponding MATLAB functions operating on the double data type, such as simplify and solve, are kept as symbolic functions in the generated MATLAB function block. The converted function block that consists of these functions cannot be used in Simulink models. You need to create your own functions with the double data type to replace these symbolic functions. If you are interested in a symbolic function that cannot be used in Simulink models, please contact MathWorks Technical Support.

Version History

Introduced in R2009a