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User defined Functions in MATLAB Part 1

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User-defined functions are similar to the MATLAB pre-defined functions. A function is a MATLAB program that can accept inputs and produce outputs. A function can be called or executed by another program or function.
Code for a function is done in an Editor window or any text editor same way as script and saved as m-file. The m-file must have the same name as the function.

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User defined Functions in MATLAB Part 1

  1. 1. User Defined Functions in MATLAB Part 1 Shameer A Koya 1
  2. 2. Introduction O User-defined functions are similar to the MATLAB pre-defined functions O A function is a MATLAB program that can accept inputs and produce outputs. O A function can be called or executed by another program or function. O Code for a function is done in an Editor window or any text editor same way as script and saved as m-file. O The m-file must have the same name as the function. 2
  3. 3. Introduction… OThe convention for naming functions is the same as for variables. OIt is important that you give meaningful variable names to variables inside a function that you write, so that you and others can understand what the function does. OThe function M-file must be saved in your current directory (otherwise it must be in the path) 3
  4. 4. Why use functions? OFunctions provide reusable code OUse same code in more than one place in program without rewriting code OReuse code by calling in different programs OMake debugging easier 4
  5. 5. Before you start … OIdentify the function ODecide the function name ODecide the input variables ODecide the output variables OFile name must be the function name. 5
  6. 6. Function Syntax function[a, b, c]= basicmath(x,y) %BASICMATH Basic Mathematical function % basicmath(x,y) is a sample matlabfunction to perform % basic mathematical operations on input variables x & y % outputs of the function are sum, difference and product % of input arguments. a = x + y; b = x – y; c = x * y; 6 Output arguments Executable code Comments about the function Name of the function Input arguments declaration statement
  7. 7. Syntax … O The declaration statement function is used to define the file as a function. O It must be typed in lower case letters. O Input arguments O Typed in side the parentheses ( ) O Used to transfer data into function from calling program. O Can be zero or more input arguments. O Output arguments O Types inside the square brackets [ ] O Used to transfer data out of function to calling program. O Can be zero or more output arguments. O Give a meaningful variable name. O Rules for giving function name is same as the rules for variable names. 7
  8. 8. More on Function Arguments O Functions have private workspaces O Variables that are created inside of a user-defined function are referred to as local variables. O They can only be accessed from inside of that function. O After the function completes its operations, the local variables are deleted from memory. O The only variable that appears in the workspace is the output of the function. O Conversely, functions cannot access variables from the workspace. (with the exception of any input parameters they might have or “global variables”---see MATLAB help on this matter).

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