User defined functions in matlab
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The document provides an overview of user-defined functions in MATLAB, explaining their structure, advantages, and types. It covers key concepts such as local and global variables, the syntax for defining functions, and introduces various types of functions including recursive, nested, and private functions. Examples of function implementations highlight practical applications, including calculating averages and quadratic equation roots.
![User Defined Functions in MATLAB
Function: A function is a group of statements that together perform a task.
In MATLAB, functions are defined in separate files. The name of the file
and of the function should be the same.
Functions operate on variables within their own workspace, which is also
called the local workspace, separate from the workspace you access at the
MATLAB command prompt which is called the base workspace.
Functions can accept more than one input arguments and may return more
than one output arguments.
Syntax of a function statement is −
function [out1,out2, ..., outN] = myfun(in1,in2,in3, ..., inN)](https://image.slidesharecdn.com/userdefinedfunctionsinmatlab-201019034201/85/User-defined-functions-in-matlab-4-320.jpg)
![Global Variables
Global variables can be shared by more than one function. For this, you need to declare
the variable as global in all the functions.I f you want to access that variable from the
base workspace, then declare the variable at the command line.
The global declaration must occur before the variable is actually used in a function. It is a
good practice to use capital letters for the names of global variables to distinguish them
from other variables.
Example
Let us create a function file named average.m and type the following code in it
−
function avg = average(nums)
global TOTAL
avg = sum(nums)/TOTAL;
end
Create a script file and type the following code in it −
global TOTAL;
TOTAL = 10;
n = [34, 45, 25, 45, 33, 19, 40, 34, 38, 42];
av = average(n)
When you run the file, it will display the following result −
av = 35.500](https://image.slidesharecdn.com/userdefinedfunctionsinmatlab-201019034201/85/User-defined-functions-in-matlab-8-320.jpg)
![Primary and Sub-Functions
Create a function file quadratic.m and type the following code in it −
function [x1,x2] = quadratic(a,b,c)
%this function returns the roots of
% a quadratic equation.
% It takes 3 input arguments
% which are the co-efficients of x2, x and the
%constant term
% It returns the roots
d = disc(a,b,c);
x1 = (-b + d) / (2*a);
x2 = (-b - d) / (2*a);
end % end of quadratic
function dis = disc(a,b,c)
%function calculates the discriminant
dis = sqrt(b^2 - 4*a*c);
end % end of sub-function
You can call the above function from
command prompt as −
quadratic(2,4,-4)
MATLAB will execute the above
statement and return the following
result −
ans = 0.7321](https://image.slidesharecdn.com/userdefinedfunctionsinmatlab-201019034201/85/User-defined-functions-in-matlab-12-320.jpg)
![Nested Functions
Example
Let us rewrite the function quadratic, from previous example, however, this time
the disc function will be a nested function.
Create a function file quadratic2.m and type the following code in it −
function [x1,x2] = quadratic2(a,b,c)
function disc % nested function
d = sqrt(b^2 - 4*a*c);
end % end of function disc
disc;
x1 = (-b + d) / (2*a);
x2 = (-b - d) / (2*a);
end % end of function quadratic2
You can call the above function from
command prompt as −
quadratic2(2,4,-4)
MATLAB will execute the above
statement and return the following
result −
ans = 0.73205](https://image.slidesharecdn.com/userdefinedfunctionsinmatlab-201019034201/85/User-defined-functions-in-matlab-14-320.jpg)
![Private Functions
Create a function quadratic3.m in your working directory and type the following
code in it −
function [x1,x2] = quadratic3(a,b,c)
%this function returns the roots of
% a quadratic equation.
% It takes 3 input arguments
% which are the co-efficient of x2, x and the constant term
% It returns the roots
d = disc(a,b,c);
x1 = (-b + d) / (2*a);
x2 = (-b - d) / (2*a);
end % end of quadratic3
You can call the above function from
command prompt as −
quadratic3(2,4,-4)
MATLAB will execute the above
statement and return the following
result −
ans = 0.73205](https://image.slidesharecdn.com/userdefinedfunctionsinmatlab-201019034201/85/User-defined-functions-in-matlab-16-320.jpg)
User defined functions in matlab
- 1. SESSION-7-8 User Defined Functions in MATLAB By: Prof. Ganesh Ingle
- 2. Course Main Topic/Chapters Introduction User Defined Functions in MATLAB Categories of Functions Summary
- 3. User Defined Functions in MATLAB Function: A function is a block of code that performs a specific task. MATLAB allows you to define functions according to your need. These functions are known as user-defined functions. Advantages : 1. The subprogram are easier to write, understand and debug. 2. A function can call itself again. It is called a recursive function. Many calculations can be done easily by using recursive functions such as calculation of factorial of a number, etc. 3. Reduction in size of program due to program code of a function can be used again and again, by calling it. 4. The complexity of the entire program can be divided into simple subtask and then function subprograms can be written for each subtask. 5. A library of a function can be designed and tested for use of every programmer. 6. Code reusability
- 4. User Defined Functions in MATLAB Function: A function is a group of statements that together perform a task. In MATLAB, functions are defined in separate files. The name of the file and of the function should be the same. Functions operate on variables within their own workspace, which is also called the local workspace, separate from the workspace you access at the MATLAB command prompt which is called the base workspace. Functions can accept more than one input arguments and may return more than one output arguments. Syntax of a function statement is − function [out1,out2, ..., outN] = myfun(in1,in2,in3, ..., inN)
- 5. Types of Functions Functions Predefined Functions Library Functions Declared in header file Body in .dll files User Defined Functions Anonymous Functions Primary and Sub-Functions Nested Functions Recursive Functions Private Functions
- 6. Types of Arguments Basically, there are two types of arguments: 1.Actual arguments: The variables declared in the function prototype or definition are known as Formal arguments 2.Formal arguments : The variable that are passed to the called function from the main function are known as Actual arguments. 3.Local Variable A local variable is a type of variable declared within programming block or subroutines. It can only be used only inside that subroutine or code block in which they were declared. The local variable exists until the block of the function is in under execution. After that, it will be destroyed automatically. 4.Global variables: Global variables are defined outside of a subroutine or function. The global variable will hold its value throughout the lifetime of a program. They can be accessed within any function defined for the program.
- 7. Types of Arguments Basically, there are two types of arguments: 1.Actual arguments: The variables declared in the function prototype or definition are known as Formal arguments 2.Formal arguments : The variable that are passed to the called function from the main function are known as Actual arguments. 3.Local Variable A local variable is a type of variable declared within programming block or subroutines. It can only be used only inside that subroutine or code block in which they were declared. The local variable exists until the block of the function is in under execution. After that, it will be destroyed automatically. 4.Global variables: Global variables are defined outside of a subroutine or function. The global variable will hold its value throughout the lifetime of a program. They can be accessed within any function defined for the program.
- 8. Global Variables Global variables can be shared by more than one function. For this, you need to declare the variable as global in all the functions.I f you want to access that variable from the base workspace, then declare the variable at the command line. The global declaration must occur before the variable is actually used in a function. It is a good practice to use capital letters for the names of global variables to distinguish them from other variables. Example Let us create a function file named average.m and type the following code in it − function avg = average(nums) global TOTAL avg = sum(nums)/TOTAL; end Create a script file and type the following code in it − global TOTAL; TOTAL = 10; n = [34, 45, 25, 45, 33, 19, 40, 34, 38, 42]; av = average(n) When you run the file, it will display the following result − av = 35.500
- 9. Example Example The following function named mymax should be written in a file named mymax.m. It takes five numbers as argument and returns the maximum of the numbers. function max = mymax(n1, n2, n3, n4, n5) %This function calculates the maximum of the five numbers given as input max = n1; if(n2 > max) max = n2; end if(n3 > max) max = n3; end if(n4 > max) max = n4; end if(n5 > max) max = n5; end You can call the function as − mymax(34, 78, 89, 23, 11)
- 10. Anonymous Functions An anonymous function is like an inline function in traditional programming languages, defined within a single MATLAB statement. It consists of a single MATLAB expression and any number of input and output arguments. You can define an anonymous function right at the MATLAB command line or within a function or script. This way you can create simple functions without having to create a file for them. The syntax for creating an anonymous function from an expression is f = @(arglist)expression Example In this example, we will write an anonymous function named power, which will take two numbers as input and return first number raised to the power of the second number. Create a script file and type the following code in it − power = @(x, n) x.^n; result1 = power(7, 3) result2 = power(49, 0.5) result3 = power(10, -10) result4 = power (4.5, 1.5) When you run the file, it displays − result1 = 343 result2 = 7 result3 = 1.0000e-10 result4 = 9.5459
- 11. Primary and Sub-Functions Any function other than an anonymous function must be defined within a file. Each function file contains a required primary function that appears first and any number of optional sub-functions that comes after the primary function and used by it. Primary functions can be called from outside of the file that defines them, either from command line or from other functions, but sub-functions cannot be called from command line or other functions, outside the function file. Sub-functions are visible only to the primary function and other sub-functions within the function file that defines them. Example Let us write a function named quadratic that would calculate the roots of a quadratic equation. The function would take three inputs, the quadratic co- efficient, the linear co-efficient and the constant term. It would return the roots.The function file quadratic.m will contain the primary function quadratic and the sub-function disc, which calculates the discriminant.
- 12. Primary and Sub-Functions Create a function file quadratic.m and type the following code in it − function [x1,x2] = quadratic(a,b,c) %this function returns the roots of % a quadratic equation. % It takes 3 input arguments % which are the co-efficients of x2, x and the %constant term % It returns the roots d = disc(a,b,c); x1 = (-b + d) / (2*a); x2 = (-b - d) / (2*a); end % end of quadratic function dis = disc(a,b,c) %function calculates the discriminant dis = sqrt(b^2 - 4*a*c); end % end of sub-function You can call the above function from command prompt as − quadratic(2,4,-4) MATLAB will execute the above statement and return the following result − ans = 0.7321
- 13. Nested Functions You can define functions within the body of another function. These are called nested functions. A nested function contains any or all of the components of any other function. Nested functions are defined within the scope of another function and they share access to the containing function's workspace. A nested function follows the following syntax − function x = A(p1, p2) ... B(p2) function y = B(p3) ... end ... end
- 14. Nested Functions Example Let us rewrite the function quadratic, from previous example, however, this time the disc function will be a nested function. Create a function file quadratic2.m and type the following code in it − function [x1,x2] = quadratic2(a,b,c) function disc % nested function d = sqrt(b^2 - 4*a*c); end % end of function disc disc; x1 = (-b + d) / (2*a); x2 = (-b - d) / (2*a); end % end of function quadratic2 You can call the above function from command prompt as − quadratic2(2,4,-4) MATLAB will execute the above statement and return the following result − ans = 0.73205
- 15. Private Functions A private function is a primary function that is visible only to a limited group of other functions. If you do not want to expose the implementation of a function(s), you can create them as private functions. Private functions reside in subfolders with the special name private. They are visible only to functions in the parent folder. Example Let us rewrite the quadratic function. This time, however, the disc function calculating the discriminant, will be a private function. Create a subfolder named private in working directory. Store the following function file disc.m in it − function dis = disc(a,b,c) %function calculates the discriminant dis = sqrt(b^2 - 4*a*c); end % end of sub-function
- 16. Private Functions Create a function quadratic3.m in your working directory and type the following code in it − function [x1,x2] = quadratic3(a,b,c) %this function returns the roots of % a quadratic equation. % It takes 3 input arguments % which are the co-efficient of x2, x and the constant term % It returns the roots d = disc(a,b,c); x1 = (-b + d) / (2*a); x2 = (-b - d) / (2*a); end % end of quadratic3 You can call the above function from command prompt as − quadratic3(2,4,-4) MATLAB will execute the above statement and return the following result − ans = 0.73205