Choose Command Syntax or Function Syntax
MATLAB® has two ways of calling functions, called function syntax and command syntax. This page discusses the differences between these syntax formats and how to avoid common mistakes associated with command syntax.
Command Syntax and Function Syntax
In MATLAB, these statements are equivalent:
load durer.mat % Command syntax load('durer.mat') % Function syntax
This equivalence is sometimes referred to as command-function duality.
All functions support this standard function syntax:
[output1, ..., outputM] = functionName(input1, ..., inputN)
In function syntax, inputs can be data, variables, and even MATLAB expressions. If an input is data, such as the numeric value
2 or the string array
["a" "b" "c"],
MATLAB passes it to the function as-is. If an input is a variable MATLAB will pass the value assigned to it. If an input is an expression, like
sin(2*pi), MATLAB evaluates it first, and passes the result to the function. If the
functions has outputs, you can assign them to variables as shown in the example
Command syntax is simpler but more limited. To use it, separate inputs with spaces rather than commas, and do not enclose them in parentheses.
functionName input1 ... inputN
With command syntax, MATLAB passes all inputs as character vectors (that is, as if they were enclosed in single quotation marks) and does not assign outputs to variables. To pass a data type other than a character vector, use the function syntax. To pass a value that contains a space, you have two options. One is to use function syntax. The other is to put single quotes around the value. Otherwise, MATLAB treats the space as splitting your value into multiple inputs.
If a value is assigned to a variable, you must use function syntax to pass the
value to the function. Command syntax always passes inputs as character vectors and
cannot pass variable values. For example, create a variable and call the
disp function with function syntax to pass the value of the
A = 123; disp(A)
This code returns the expected result,
You cannot use command syntax to pass the value of
A, because this call
is equivalent to
Avoid Common Syntax Mistakes
Suppose that your workspace contains these variables:
filename = 'accounts.txt'; A = int8(1:8); B = A;
The following table illustrates common misapplications of command syntax.
|This Command...||Is Equivalent to...||Correct Syntax for Passing Value|
Passing Variable Names
Some functions expect character vectors for variable names, such as
whos. For example,
whos -file durer.mat X
requests information about variable
X in the example file
durer.mat. This command is equivalent to
How MATLAB Recognizes Command Syntax
Consider the potentially ambiguous statement
This could be a call to the
ls function with
'./d' as its argument. It also could represent element-wise
division on the array
ls, using the variable
as the divisor.
If you issue this statement at the command line, MATLAB can access the current workspace and path to determine whether
d are functions or variables.
However, some components, such as the Code Analyzer and the Editor/Debugger, operate
without reference to the path or workspace. When you are using those components,
MATLAB uses syntactic rules to determine whether an expression is a function
call using command syntax.
In general, when MATLAB recognizes an identifier (which might name a function or a variable), it analyzes the characters that follow the identifier to determine the type of expression, as follows:
An equal sign (
=) implies assignment. For example:
An open parenthesis after an identifier implies a function call. For example:
Space after an identifier, but not after a potential operator, implies a function call using command syntax. For example:
Spaces on both sides of a potential operator, or no spaces on either side of the operator, imply an operation on variables. For example, these statements are equivalent:
ls ./ d ls./d
Therefore, MATLAB treats the potentially ambiguous statement
as a call to the
ls function using command syntax.
The best practice is to avoid defining variable names that conflict with common functions, to prevent any ambiguity.