Computer Programming in MATLAB

Transcription

1 Computer Programming in MATLAB Prof. Dr. İrfan KAYMAZ Atatürk University Engineering Faculty Department of Mechanical Engineering

2 User Defined Functions MATLAB has a number of built-in (compiled) functions, e.g. sin, sqrt, sum. If you find that you are often building a function from several Matlab commands, you can develop a user-defined function that can be used in a same way as the built-in Matlab functions.

3 User Defined Functions Syntax function [output variables] = function_name(input variables); defines function function_name that accepts inputs variables and returns outputs variables. The rules for writing an M-file (user defined) function are the following: 1- The first line of a function has to be the following syntax: function [output variables] = function_name(input variables); 2- Function written to an m-file must be saved with the same name of «function_name» 3- A user-defined function is called by the name of the m-file.

4 Example 1 Write a function that computes the final velocity of a free-falling object. Function file (file name sonhiz.m) (subprogram) function v= sonhiz(g,h) % file must be named with sonhiz v=sqrt(2*g*h); m_file (Main program) clc clear all g=9.81; h=10; v=sonhiz(g,h)

5 Example 2 Write a function that computes the the area and perimeter of a cicrcle. Function file (file name circle.m) (subprogram) function [area,perimeter]=circle(r) area=pi*r^2; perimeter=2*pi*r; M_file (Main program) clc clear all R=1; [area,perimeter]=circle(r)

6 Example 3 Write a function that computes the distance between two points x1= x coordinate of the first point; x2= x coordinate of the second point y1= y coordinate of the first point; y2= y coordinate of the first point Function file (dis.m) (subprogram) function distance= dis(x1,y1,x2,y2) distance=sqrt((x2-x1).^2+(y2-y1).^2); m_file (Main Program) clc clear all x1=3; y1=4; x2=1; y2=2; distance= dis(x1,y1,x2,y2); fprintf('distance between two points=%g\n',distance);

7 Example 4 Write a MATLAB program that computes the value of the following equation according to the x and y received from keyboard. F(x,y)=x 2 y+x.y+ ln(x)+1 log 10 (y) +tan(x y )

8 Example 5 Write a MATLAB program to solve the value of the following equation for x from 3 to 13 by increments of 0.1, and then plots the x and y data in the main m-file. The values of the variables must be given in the main m-file, a=5, b=6, and c=8

9 Solution 5 Main m-file (Named with: soru.m ) clc clear all x=3:0.1:13 a=5;b=6;c=8; y=deneme(a,b,c,x); plot(x,y) Function File (Named with deneme.m) function y=deneme(a,b,c,x); y=a+(b*x.^2)/2+(c*exp(x)+2)/3;

10 Example 6 Write a Matlab program to find the sum and mean of the successive odd integers from 1 to 35, and print the results in the following format. Sum of numbers =324 Mean of numbers =18

11 IO When you get into serious programming, you will often need to store data on a disk. The process of moving data between MATLAB and disk files is called importing (from disk files) and exporting (to disk files). Direct input of data from keyboard becomes impractical when the amount of data is large and the same data is analyzed repeatedly. In these situations input and output is preferably accomplished via data files. The process of moving data between MATLAB and disk files is called importing (from disk files) and exporting (to disk files).

12 File open: fopen fopen, opens a file or obtain information about open files. Syntax fid = fopen( filename, permission ) opens the file filename in the mode specified by permission and returns fid, the file identifier. fid-> file identifier filename -> file name permission -> r,w,.., etc.

13 File open: fopen 'r' 'w' 'a' 'r+' 'w+' 'a+' Open file for reading (default). Open or create new file for writing. Discard existing contents, if any. Open or create new file for writing. Append data to the end of the file. Open file for reading and writing. Open or create new file for reading and writing. Discard existing contents, if any. Open or create new file for reading and writing. Append data to the end of the file. Atatürk University

14 File close: fclose fclose closes one or all open files. Syntax status = fclose(fid); fid-> file identifier Status-> if succesful 0; otherwise -1.

15 Writing data to a file: fprintf Write formatted data to file. Syntax: fprintf(fid,format,a,...) fprintf (fid, %format%format%format.,var_1,var_2,var_3,.)

16 Example 7 Write a MATLAB program that writes the following M array to a file named with «veri.dat» With for loop M=[ ]; a=fopen('veri.dat','w'); fprintf (a,'%d %d %d %d',m); fclose(a); M=[ ]; a=fopen('veri.dat','w'); for i=1:4 fprintf(a,'%d ',M(i)); end fclose(a);

17 Example 8 Write a MATLAB program that writes the following M matrix to a file named with «veri.dat» A=[ ; 2 4 5]; a=fopen('veri.dat','w+'); for i=1:2 for j=1:3 fprintf(a,'%d ',A(i,j)); end end fclose(a); Atatürk University

18 Reading data from a file: fscanf fscanf: fscanf reads formatted data from a file Syntax [value, number_of_values_read] = fscanf(file_variable, 'format', count); value : The returned information is the value number_of_values_read : the number of values actually read count : Amount of data to read: n, [n, m], Inf

19 Example 9 Write a MATLAB program that reads the all data from a file named with «veri.dat» and assigns them to b variable. veri.dat clear all clc a=fopen ('veri.dat', 'r' ); [b,sayi]=fscanf(a,'%d ',inf); fclose(a); b Atatürk University

20 Example 10 Write a MATLAB program that reads the first two data from a file named with «veri.dat» and assigns them to b variable. veri.dat clear all clc a=fopen ('veri.dat', 'r' ); for i=1:2 b(i)=fscanf(a,'%d ',[1]); end fclose(a); b Atatürk University

21 Reading data from a file to more than one variable Veri.dat To read the data from the file which is in the same format with the left side; a = fopen('veri.dat', 'r'); b = fscanf(a, '%g %g', [2 inf]); fclose(a) RESULT is To assign the rows to different variables c=b(1,:) d=b(2,:) To read the data direcly from the file a=fopen('veri.dat','r') for i=1:6 d(i)=fscanf(a,'%f',[1]); e(i)=fscanf(a,'%f',[1]); end fclose(a) Atatürk University

22 Reading data from a file to more than one variable Another method; Veri.dat clc clear all a=fopen('veri.dat','r'); for i=1:6 for j=1:2 masa(i,j)=fscanf(a,'%g',[1,1]); end end fclose(a); k=(masa(:,1))' % tırnak işareti transpoz işlemidir t=(masa(:,2))'

23 Example 11 In a cargo company, a pricing policy according to the package weight is as follows; Base price is 5 TL for packages up to 2 kg. For the packages heavier than 2 kg, 0.5 TL should be added to the base price for every 1 kg. If the packages is heavier than 35 kg, 10 TL should be added to the total price. The packages heavier than 50 kg are not accepted because of worker s health. Write a Matlab program that computes the price according to the above-mentioned scheme and then writes the following table for 1:50 kg pacages to a file named with veri.dat. (Assume that the scale readings are only integer values) Ağırlık (kg) Fiyat (TL)