Matlab Scripts and Functions Reading Review, Lecture notes of Programming for Engineers

Download Matlab Scripts and Functions Reading Review and more Lecture notes Programming for Engineers in PDF only on Docsity! 6/21/2018 1 C/C++ Programming for Engineers: Matlab Scripts and Functions John T. Bell Department of Computer Science University of Illinois, Chicago 2 Reading Review Which of the following would multiply the cosine of X times the common logarithm of X, when X is given in degrees? A. cos( X ) * log( X ) B. cos( X ) * log10( X ) C. cosd( X ) * log( X ) D. cosd( X ) * log10( X ) E. cos( X degrees ) * commonLog( X degrees ) 6/21/2018 2 3 Matlab Script Files • Any command that can be run in Matlab can be placed in an ordinary text file ( with a .m extension ) and run as a Matlab script. • The easiest way to do this is to use Matlab’s built-in editor and drag commands from command history into the script, & then edit. • Run the script by typing the script name, or by pressing the “run” button in the script editor. 4 Special Characters in Scripts • The % percent sign is used to create comments, from the % to the end of the line. – %{ Large block comments in braces and % %} • The ; semi-colon at the end of the line suppresses the display of the command. • Three dots, … , at the end of a line … are used to continue … long lines onto the next line. 6/21/2018 5 9 Formatted Output in Matlab • The fprintf( ) command prints strings: – fprintf( ‘This program plots sine waves.’ ); • New lines start (only) when \n is printed: – fprintf( ‘This will print’ ); – fprintf( ‘ all on one line.\n’ ); • This will print all on one line. – fprintf( ‘This will print\n on\n three lines.\n’ ); • This will print • on • three lines. 10 Format Specifiers in fprintf( ) • Whenever a % is encountered in the output string, fprintf( ) prints a data value: – fprintf( ‘The result is %f mpg.\n’, mileage ); 6/21/2018 6 11 Format Specifiers in fprintf( ) Operator Prints Description %f fixed-point f is for fixed-point. %d integer d is for decimal integer. The use of 'd' is due to historical reasons, and is slightly misleading because a decimal number could have a fractional part. In MATLAB, %d means decimal integer which does not have a fraction. %i integer i is for integer. This operator is identical to %d when formatting output. %c character c is for character. %s string s is for string. 12 Special Characters Special character Description \n Prints a new line. '' Two single quotation marks print a single quotation mark. Note that a single quotation mark alone would instead indicate the end of the format string. %% Two percent characters print one percent character. Note that a single % character would instead indicate the start of a formatting operator like %f. \\ Two backslash characters print one backslash character. Note that a single backslash character would instead indicate the start of a special character sequence like \n. \t Prints a tab. 6/21/2018 7 13 Floating Point Formats Operator Description %f Fixed-point notation, 109.42 %e Scientific notation with lowercase e, as in 6.02e+23, 3.141593e+00 %g Either %f or %e, whatever is shorter %E Scientific notation with capital E, as in 6.02E+23, 3.141593E+00 %G Either %G or %E, whichever is shorter, 6.02E+23, 3.141593 Table 3.6.1: Floating-point number formatting operators. 14 Preview What happens if a Matlab workspace contains a variable X, and then a script is run that creates a new variable X and gives it a value? A. There will now be two variables named X. B. The workspace X will be wiped out, and replaced with a new X. C. The X created in the script will only exist while the script runs, and will then disappear. D. The script X will be automatically given a different name. E. An error will occur, since two variables can’t have the same name. 6/21/2018 10 19 Matlab Function Outputs • The [ out1, out2, … ] = format is for functions that return multiple results. – If a function returns a single result, the [ ] square brackets are not required. – If a function does not return any results, then the equals sign should also be omitted. • The program that called the function gets its results through the output parameters. 20 Matlab Function Help Comments • Every Matlab function should contain a “help” comment, which is the first comment block after the “function” line. • The help comment is displayed whenever one types “help” for the function in question. ( The first line is displayed by lookfor. ) function [ finBalance, interest ] = BalanceWithInterestBoth( rate, initBalance ) % Calculates the final balance of an investment with compound interest. % Inputs: rate -- Interest rate, initBalance -- Initial balance. % Output: finBalance -- Final balance. 6/21/2018 11 21 Matlab Function Operation • The code within a Matlab function is basically the same as a Matlab script. • Sometime before the function returns, it must assign values to all the output parameters. • The ‘return;’ statement ceases execution of the function, and returns control back to the calling program. No function code is executed after a return statement. 22 Calling Matlab Functions • User-written Matlab functions are called by name, the same way that Matlab library functions are called. • Values or variables must be passed in to the function input parameters. • Variables must be provided to receive the output results.