Chapter 6: User defined functions and function files

Transcription

1 The Islamic University of Gaza Faculty of Engineering Civil Engineering Department Computer Programming (ECIV 2302) Chapter 6: User defined functions and function files ١

2 6.1 Creating a function file Input data Function File output Function files are created and edited like script files. ٢

3 6.2 Structure of a function file Function definition line The H1 line Help text Function body Assignment of values to output arguments ٣

4 6.2.1 Function Definition Line The first line in a function file must be the function definition line. Defines the file as a function file Defines the name of the function Defines the number and order of the input and output arguments. function [output arguments] = function_name(input arguments) ٤

5 6.2.2 Input and output arguments In order for the function file to work, the output arguments must be assigned values in the computer program that is in the function body. Function definition line function[mpay,tpay] = loan(amount,rate,years) function [A] = RectArea(a,b) function A = RectArea(a,b) function [V,S] = SphereVolArea(r) function trajectory (v,h,g) Comments 3 input arguments, 2 output arguments 2 input arguments, 1 output argument 1 input argument can be typed without brackets. 1 input argument, 2 output variables. 3 input arguments, no output arguments ٥

6 6.2.3 The H1 line and Help text lines They are optional, but used to provide information about the function Function Body The function body contains the code that performs the computation. The code can use all MATLAB features. ٦

7 6.3 Local and Global Variables If you want more than one function to share a single copy of a variable, simply declare the variable as global in all the functions. The global declaration must occur before the variable is actually used in a function. Example: function h = falling(t) global GRAVITY h = 1/2*GRAVITY*t.^2; ٧

8 6.4 Saving a function File A function file must be saved before it can be used. It is recommended that the file is saved with the name that it is identical to the function name in the definition line. Function definition line function[mpay,tpay] = loan(amount,rate,years) function [A] = RectArea(a,b) function A = RectArea(a,b) function [V,S] = SphereVolArea(r) function trajectory (v,h,g) Function name loan.m RectArea.m RectArea.m SphereVol.m Rajectory.m ٨

9 6.5 Using a user defined function Two of the ways that a function can be used: First input argument is loan amount Second input argument is interest rate, And third input argument is the number of years ٩

10 Example 1 ١٠

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12 Example 2 ١٢

13 6.7 Comparison between script files and function files M files (both) The first line in a function file is the function definition line. The variables in a function file are local. The variables in a script file are recognized in the command window. Script files can use variables that have been defined in the workspace. Function files can accept data through input arguments and can return data through output arguments. When a function file is saved, the name of the file should be the same as the name of the function. ١٣

14 6.8 Anonymous and inline functions Anonymous function Is a simple (one line) a user defined function that is defined and written within the computer code (not in a separate function file). It can be defined in any part of MATLAB in: Command window Script file Inside user defined functions. (arglist) expr ١٤

15 Examples: >> Cube x^3; >> Circle 16*x^2+9*y^2; >> a, b, and c are defined (assigned numerical values) >> parabola a*x^2+b*x+c Note: anonymous function can include preassigned variables (e.g a, b) ١٥

16 Example (single input argument): ١٦

17 Example (several independent arguments): See Sample problem 6.3 P 168 ١٧

18 6.8.2 Inline Function Note: Name= inline( math expression typed as string ) inline function can not include preassigned variables. ١٨

19 Inline Function has two or more independent variables: Name= inline( math expression typed as string, arg1, arg2, arg3 ) Note: This format shows the order of the arguments to be used when calling the function. If the independent variables are not listed in the command, MATLAB arranges the arguments in alphabetic order. ١٩

20 6.9 Function Functions A (function A) works on uses another function (function B) Using function handles for passing a function into a function function For built-in and user-defined functions: A function handle is created by typing the in front of the function name. For example The function handle can be assigned to a variable name. The next example shows writing a function function that accepts a function handle as an input argument ٢٠

21 1. Passing a user defined function into a function function ٢١

22 ٢٢

23 2. Passing an anonymous function into a function function ٢٣

24 6.9.2 Using a function Name for Passing a Function into a Function By typing the name of the function that is being imported as a string in the input argument of the function. This method for user defined functions. Function handles are easier and more efficient. When a user defined function is imported by using its name, the value of the imported function inside the function function has to be calculated with the feval command. There is a difference in the way that the code in the function function is written that depends on how the imported function is passed in. ٢٤

25 Examples on using the feval command ٢٥

26 1. Writing a function function that accepts a function by typing its name as an input function ٢٦

27 ٢٧

28 6.10 Subfunctions A function file contain more than one user defined function. The functions are typed one after the other. The first function is called the main function and the rest of the functions are called subfunctions. The subfunctions can be typed in any order. The name of the function file correspond the name of the main function. Inside the function file, each of the functions can call any of the other functions. ٢٨

29 Example: Average and standard deviation ٢٩

30 6.11 Nested functions A nested function is a user-defined function that is written inside another user defined function. An end statement is required at the end of all functions. The variables defined in any function can be read and redefined in the rest functions and vise versa. The functions can call each other. One Nested function function y = A(a1,a2).. function z = B(b1,b2) end. end ٣٠

31 Two or more Nested function function y = A(a1,a2).. function z = B(b1,b2) end function w = C(c1,c2) end The three functions can access the workspace of each other. The three functions can call each other.. end ٣١

32 Example: Nested function ٣٢

33 Two levels of nested function function y = A(a1,a2).. function z = B(b1,b2) function w = C(c1,c2) end.. end function u = D(d1,d2) function h = E(e1,e2) end.. end. end A nested function can be called from a level above it. A nested function can be called from a nested function at the same level within a primary function. A nested function can be called from a nested function at any lower level. ٣٣

34 Problem 6.5 ٣٤

35 Problem 6.10 ٣٥

36 Problem 6.21 ٣٦

37 Example Given: An object thrown vertically with a speed v 0 reaches a height h at time t where: 1 h v0t gt 2 Required Write a function to compute h given v 0 and t. It should allow t to be a vector. Use the function to PLOT h versus t for t between 0 and 10s and v 0 = 50 m/s. 2

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