define assignment in matlab

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• Yossi Farjoun

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Introduction to matlab programming, user-defined functions.

We have just seen—above, using the \(@(x)\) notation—an example of how to create simple user-defined functions. This notation can only have one line of code, and oftentimes that can be insufficient for the task at hand. We have also seen scripts files, in which we can put many lines of code and then “call” the script to have MATLAB® execute the lines in that script. So what’s a function and how is it different from a script?

A function is also a file with lines of code, but there are several distinctions between a function and a script:

When we “call” a function we usually give it input and expect output. For example:

We gave the input pi/2 to the function sin and assigned the output to the variable a . The function sin is not written in MATLAB code, so we cannot see how it is implemented, though on occasion it can be useful to see how some MATLAB functions are implemented. For example the function randperm(n) returns a random ordering of the numbers 1:n . It is implemented in MATLAB and can be viewed by writting open randperm (your copy of MATLAB might have a different implementation, but here’s mine):

Notice that the first line starts with the keyword function , which states that this file contains a function rather than a script. Next comes the declaration of the return value p . This means that the value of the variable, p when this function terminates, will be returned as the output of the function. Next comes the name of the function. This should match the name of the file. Now the list of input variables, only one in this case: n . So whatever the input is when the function is called, internally it will be placed in a variable called n . Next there’s a long comment block which becomes the help file text (type help randsort and see) and finally the actual body of the function. In this case it is one line of code, but it is slightly strange; it turns out that you can return more than one value from a function. The function sort normally returns the inputs vector sorted:

But if you ask for two output variables, sort will also tell you the permutation needed to get from the input to the output:

As this code uses the random number generator ‘rand’, the results you get may be different from these.

As the original list of numbers is random, it implies that the permutation needed to sort it is a random, uniformly distributed permutation, and this is what MATLAB returns as the output of the function randperm . Notice the use of the tilde character to signify that the first return value isn’t needed. This is a new expansion of the MATLAB language. If you have an old version, the code will have a “throw-away” variable (a variable that is not used).

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In MATLAB environment, every variable is an array or matrix.

You can assign variables in a simple way. For example,

MATLAB will execute the above statement and return the following result −

It creates a 1-by-1 matrix named x and stores the value 3 in its element. Let us check another example,

Please note that −

Once a variable is entered into the system, you can refer to it later.

Variables must have values before they are used.

When an expression returns a result that is not assigned to any variable, the system assigns it to a variable named ans, which can be used later.

For example,

You can use this variable ans −

Let's look at another example −

Multiple Assignments

You can have multiple assignments on the same line. For example,

I have forgotten the Variables!

The who command displays all the variable names you have used.

The whos command displays little more about the variables −

• Variables currently in memory
• Type of each variables
• Memory allocated to each variable
• Whether they are complex variables or not

The clear command deletes all (or the specified) variable(s) from the memory.

Long Assignments

Long assignments can be extended to another line by using an ellipses (...). For example,

The format Command

By default, MATLAB displays numbers with four decimal place values. This is known as short format .

However, if you want more precision, you need to use the format command.

The format long command displays 16 digits after decimal.

For example −

MATLAB will execute the above statement and return the following result−

Another example,

The format bank command rounds numbers to two decimal places. For example,

MATLAB displays large numbers using exponential notation.

The format short e command allows displaying in exponential form with four decimal places plus the exponent.

The format long e command allows displaying in exponential form with four decimal places plus the exponent. For example,

The format rat command gives the closest rational expression resulting from a calculation. For example,

Creating Vectors

A vector is a one-dimensional array of numbers. MATLAB allows creating two types of vectors −

• Row vectors
• Column vectors

Row vectors are created by enclosing the set of elements in square brackets, using space or comma to delimit the elements.

Column vectors are created by enclosing the set of elements in square brackets, using semicolon(;) to delimit the elements.

Creating Matrices

A matrix is a two-dimensional array of numbers.

In MATLAB, a matrix is created by entering each row as a sequence of space or comma separated elements, and end of a row is demarcated by a semicolon. For example, let us create a 3-by-3 matrix as −

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A variable in simple terms is a storage place that has some memory allocated to it. Basically, a variable used to store some form of data. Different types of variables require different amounts of memory and have some specific set of operations that can be applied to them. The Matlab workspace store all the variables that you create or use during a session. 

Creating Variables

To create a variable enter the name of the variable in the command window, followed by an = operator, and then assign it some values .

Example: 

  Output:

  Note:  

• If you don’t put ‘;’ after the variable name, Matlab will display its content after hitting enter.
• If you don’t give any name to your variable by default Matlab name it with an answer.
• By default, Matlab treats all variables as matrices if you write just 1 it will store it as 1×1 matrix.

To display the content of the Matlab variable you just need to type the name of the variable, and it will show its content on Command-Line:

  Example:

Multiple Assignments of Variables

We can also define the multiple variables in a single line using “;” operator.

Who command

Who lists in alphabetical order the names of all variables in the currently active workspace. To use this command variables should be present in the active workspace and memory allocated to each variable is necessary.

Assigning Vectors to variables

A vector is a one-dimensional array of numbers. Matlab allows you two types of vector: 

• Column Vector.

Row Vectors are created by enclosing numbers in square brackets separating with either space or comma.

Column Vectors are created by enclosing numbers in square brackets, separating each number with ;(semicolon).

Assigning Matrices to variables

A Matrix is a two-dimensional array of numbers. In Matlab, matrices are created by enclosing numbers in a square bracket write each row of numbers with space or comma separate and after each row put a semicolon. The below code will create a 3×3 matrix:

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How to Write a Function and Call It in MATLAB

Last Updated: May 29, 2023

wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, volunteer authors worked to edit and improve it over time. This article has been viewed 87,009 times. Learn more...

Functions are the basis of all scripting and programming languages. With functions, you can make your applications do anything you want. Functions are very useful and necessary in all applications that are design in MATLAB. We will be designing the math function y = mx+ b which is known as the slope equation this equation if programmatically defined is helpful since we can just plug in the known inputs and the program will output the answer. This instruction set assumes you have basic knowledge of MATLAB, such as how to open a script file and how to perform simple data operations.

Things You Should Know

• Start your script with function , followed by the name you want to assign it.
• After writing your function in the script editor, you can call it using the format yourfunction(inputvalue1, inputvalue2, inputvalueN ).
• Adding comments to your script makes it easy for anyone to understand the purpose of each input.

Community Q&A

• Do not forget the semicolon when defining your equation this will suppress the output which means it will not output the number before you want it to be outputted to the user Thanks Helpful 1 Not Helpful 0
• In other programming language the new line character is "/n"; in MATLAB it is "\n". Thanks Helpful 0 Not Helpful 0
• If you do not save your program it will not work, or when you execute or call your function nothing will happen. Thanks Helpful 0 Not Helpful 0
• For every Matlab function you create you must add a END to it this is crucial and your program will not work otherwise. Thanks Helpful 0 Not Helpful 0

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How do I define a variable without assigning it a value?

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How do I set default values for functions parameters in MATLAB?

Is it possible to have default arguments in MATLAB?

For instance, here:

I would like to have the true solution be an optional argument to the wave function. If it is possible, what is the proper way to do this?

Currently, I am trying what I posted above and I get:

17 Answers 17

There isn't a direct way to do this like you've attempted.

The usual approach is to use "varargs" and check against the number of arguments. Something like:

There are a few fancier things you can do with isempty , etc., and you might want to look at MATLAB central for some packages that bundle these sorts of things.

You might have a look at varargin , nargchk , etc. They're useful functions for this sort of thing. varargs allow you to leave a variable number of final arguments, but this doesn't get you around the problem of default values for some/all of them.

I've used the inputParser object to deal with setting default options. MATLAB won't accept the Python-like format you specified in the question, but you should be able to call the function like this:

After you define the wave function like this:

Now the values passed into the function are available through i_p.Results . Also, I wasn't sure how to validate that the parameter passed in for ftrue was actually an inline function, so I left the validator blank.

• 7 As best I can tell, this , is the preferred method. It's clean, self-documenting (more so an a bunch of if nargin statemens), easy to maintain, compact, and flexible. –  JnBrymn Commented Mar 7, 2011 at 14:02
• the complexity Matlab adds to every step one takes is just crazy. –  spaceKelan Commented May 8 at 10:17

Another slightly less hacky way is

• This option doesn't work if you are going to use MATLAB Coder to generate C code, as Coder does not support the "exist" function. –  Dave Tillman Commented Mar 9, 2018 at 16:20

"True" default arguments (i.e. defaults via a purpose-built language feature rather than parsing functions or hand-rolled code) were introduced in 2019b with the arguments block .

As a simplified example, consider the following function:

c is an optional input with a default value of 0. Inputs a and b have no defaults defined making them required inputs.

myFun may now be called with or without passing a value for c, with the default value of c=0 being used if no value is provided.

• 1 why no body vote for this answer? –  Dongdong Kong Commented Jun 7, 2022 at 3:48
• 1 This answer wasn't a feature in Matlab when the question was originally answered but is now the correct solution –  Tasty213 Commented Dec 16, 2022 at 11:58
• Sorting the answers by "Trending" finally payed off. –  flor.debois Commented Mar 27, 2023 at 11:48

Yes, it might be really nice to have the capability to do as you have written. But it is not possible in MATLAB. Many of my utilities that allow defaults for the arguments tend to be written with explicit checks in the beginning like this:

Ok, so I would generally apply a better, more descriptive error message. See that the check for an empty variable allows the user to pass in an empty pair of brackets, [] , as a placeholder for a variable that will take on its default value. The author must still supply the code to replace that empty argument with its default value though.

My utilities that are more sophisticated, with many parameters, all of which have default arguments, will often use a property/value pair interface for default arguments. This basic paradigm is seen in the handle graphics tools in MATLAB, as well as in optimset, odeset, etc.

As a means to work with these property/value pairs, you will need to learn about varargin , as a way of inputting a fully variable number of arguments to a function. I wrote (and posted) a utility to work with such property/value pairs, parse_pv_pairs.m . It helps you to convert property/value pairs into a MATLAB structure. It also enables you to supply default values for each parameter. Converting an unwieldy list of parameters into a structure is a very nice way to pass them around in MATLAB.

This is my simple way to set default values to a function, using "try":

I am confused nobody has pointed out this blog post by Loren, one of MATLAB's developers. The approach is based on varargin and avoids all those endless and painful if-then-else or switch cases with convoluted conditions. When there are a few default values, the effect is dramatic . Here's an example from the linked blog:

If you still don't get it, then try reading the entire blog post by Loren. I have written a follow-up blog post which deals with missing positional default values. I mean that you could write something like:

and still have the default eps value for the tol parameter (and @magic callback for func of course). Loren's code allows this with a slight, but tricky modification.

Finally, just a few advantages of this approach:

• Even with a lot of defaults the boilerplate code doesn't get huge (as opposed to the family of if-then-else approaches, which get longer with each new default value)
• All the defaults are in one place. If any of those need to change, you have just one place to look at.

Truth be told, there is a disadvantage too. When you type the function in MATLAB shell and forget its parameters, you will see an unhelpful varargin as a hint. To deal with that, you're advised to write a meaningful usage clause.

• The link to your follow-up blog post is broken; can you fix it? –  equaeghe Commented Jan 9, 2017 at 10:30
• 1 This answer needs more visibility. I remembered the blog post from Loren, and was looking for it, and opened this stackoverflow question in the hope I would find it easily that way. –  MacroController Commented Nov 19, 2020 at 23:14
• > The link to your follow-up blog post is broken; can you fix it? <br/> web.archive.org/web/20160711181129/http://all3fox.github.io/… –  alisianoi Commented Jan 29, 2022 at 22:52

There is also a 'hack' that can be used although it might be removed from MATLAB at some point:

Function eval actually accepts two arguments of which the second is run if an error occurred with the first.

Thus we can use

to use value 1 as the default for the argument.

Here is a nifty way to deal with this issue, taking up only three lines of code (barring line wraps). The following is lifted directly from a function I am writing, and it seems to work as desired:

I've found that the parseArgs function can be very helpful.

Here's its documentation:

Helper function for parsing varargin . Makes it easy to write functions that take arguments like this: subaxis(4,2,1,'spacing',0,'marginleft',.1,'H','pt',.1)

ArgStruct=parseArgs(varargin,ArgStruct[,FlagtypeParams[,Aliases]])

• ArgStruct is the structure full of named arguments with default values.
• Flagtype params is params that don't require a value. (the value will be set to 1 if it is present)
• Aliases can be used to map one argument-name to several argstruct fields

example usage:

• Can you elaborate? –  Peter Mortensen Commented Mar 23, 2021 at 16:43
• I've pasted in the documentation. It shows a sketch of how to use it to set default values. –  Mr Fooz Commented Mar 23, 2021 at 17:23

After becoming aware of ASSIGNIN (thanks to this answer by b3 ) and EVALIN I wrote two functions to finally obtain a very simple calling structure:

Here's the listing:

This is more or less lifted from the MATLAB manual ; I've only got passing experience...

• 1 There were a couple of errors in the code that I corrected. First, "optargin" needs to be defined. Second, "varargin" is a cell array that collects all subsequent inputs, so you have to use cell array indexing to remove values from it. –  gnovice Commented Apr 28, 2009 at 2:33
• I need to get my vision checked; I swear I saw none of that in the manual yesterday :( –  kyle Commented Apr 29, 2009 at 18:44
• @kyle: Not to worry, we all make mistakes. That's why I like SO's wiki-ish style: if I make some silly typo, there's usually someone else around who can catch it and fix it quickly for me. =) –  gnovice Commented Apr 29, 2009 at 19:29

Matlab doesn't provide a mechanism for this, but you can construct one in userland code that's terser than inputParser or "if nargin < 1..." sequences.

Then you can call it in your functions like this:

The formatting is a convention that lets you read down from parameter names to their default values. You can extend your getargs() with optional parameter type specifications (for error detection or implicit conversion) and argument count ranges.

There are two drawbacks to this approach. First, it's slow, so you don't want to use it for functions that are called in loops. Second, Matlab's function help - the autocompletion hints on the command line - don't work for varargin functions. But it is pretty convenient.

• Please don't edit this answer to put "MATLAB" in all caps. I realize that's the official styling for it, but it seems like shouting to me, so I don't use it in my own writing. –  Andrew Janke Commented Mar 23, 2021 at 16:53

If you would use Octave you could do it like this - but sadly MATLAB does not support this possibility:

(Taken from the documentation .)

You might want to use the parseparams command in MATLAB; the usage would look like:

E.g., f(2,4,'c',3) causes the parameter c to be 3.

I like to do this in a somewhat more object-oriented way.

Before calling wave(), save some of your arguments within a struct, e.g. one called parameters:

Within the wave function then check, whether the struct parameters contains a field called 'flag' and if so, if its value is non empty. Then assign it either a default value you define before, or the value given as an argument in the parameters struct:

This makes it easier to handle large numbers of arguments, because it does not depend on the order of the given arguments. That said, it is also helpful if you have to add more arguments later, because you don't have to change the functions signature to do so.

• Why not follow the MATLAB standard of name-value pairs? wave(a,b,'flag',42,'fTrue',1) –  Cris Luengo Commented May 24, 2018 at 13:32
• This is certainly an option as well, especially when one has only few parameters. Calling wave() with a big number of name-value pairs, however, might reduce the readability of the code. I therefore often prefer to group certain inputs into structs. –  CheshireCat Commented May 25, 2018 at 12:50

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