101
Lecture Engineering 37 MATLAB I/O
Prof. Michael Falk University of Michigan, College of Engineering
Announcements
Project 8, Due Tonight at 9pm Also on paper in your lab section Thurs/Fri. Sample output can be found in the Resources/Projects part of the Ctools Site. Clarification:
If a colony has 2 or more neighbors with the same, highest
value of fitness that are of different types, the colony does not change.
Friday: Exam 4 Review Monday: Super Quiz - no 3 point limit (approx 10 clicker questions all on MATLAB)
More Announcements
Exam 4 will take place Fri, Dec 15 from 8-10am. Samples of Exam 4 have now been posted Section 201, 203 EECS 1500 Section 202 EECS 1301 Sections 204, 205 EECS 1311 Section 206 EECS 1303 Sections 207, 208 IOE 1610 Section 209 IOE 1680 If you have a conflict with this time contact me by this Friday. The alternate exam time for those with exam conflicts only is Fri, Dec 15 from 10:30-12:30 in EECS 1500
Yet More Announcements
Returned work and regrades:
Remember that you cannot turn in regrade requests to your GSI more than 1 week after the paper is returned in your lab section. Furthermore Dec 15 (on your way into the final exam) is the last day for regrade requests and to turn in time sheets if you have been doing tutoring to earn an A+ in the class.
Project 5 and 6 regrade requests must be turned in this week (deadline depends on which day your GSI handed Project 5 and/or 6 back in section). Project 7 will be returned this week Thursday/Friday and can only be turned in for regrade up until Dec 15. Project 8 will be available for pickup next week Tuesday and can only be turned in for regrade up until Dec 15. Exam 3 will be returned this week Tues/Weds and can only be turned in for regrade up until Dec 12/13.
Course Evaluations
Please take the time to write general comments on the back of the form. I read all comments and take them into account. I am particularly interested in finding out the following:
1.
2. 3. 4. 5.
6.
Did you find answering PRS questions during class useful for your in-class learning? Did you regularly consult with your assigned discussion group during PRS questions? Did you work with people you met in your PRS discussion group on projects or while studying outside of class? Do you think you would have met these people without being assigned to a group, ie if seating was self-selected? Would you have preferred self-selected seating? How strongly do you feel that way? Did you find the Project topics interesting? Are there any that you thought were particularly good or bad?
Input/Output in MATLAB
There are a number of ways you can handle input from keyboard and files as well as output to screen and files. Simple I/O: disp and input Formatted output: fprintf Storing data in files simply: save/load General file input/output: fopen, fscanf, fprintf and fclose.
disp/input
The most straightforward way to incorporate input/output into MATLAB programs is to use display and input. disp( data ) will output the data to the screen. Unlike display() which is called after any command that does not end with a semicolon, disp() does not put a "data =" message before the output.
disp()
Example: x = [5 : 9]; disp(x); Output: 5 6 7 8 9
disp()
Example: name = `Zarathustra'; disp([ `My name is ` name]); Output: My name is Zarathustra
input()
The easiest way to get input from the user is the input() command. The input(question) command prints the question and then returns the input read from the user via the keyboard.
input()
Example: num = input( ` How many? `); disp([ ` You want ` num ` ?']); Output: How many? 10 You want 10 ?
Exercise 1
Which program will output the following 3 rows of text?
00000000011111111112222222 12345678901234567890123456 abcdefghijklmnopqrstuvwxyz
Exercise 1
00000000011111111112222222 12345678901234567890123456 abcdefghijklmnopqrstuvwxyz
3. letters = char([0 :25]+ 'a') ; ones = char(mod([1 :26],10)+'0') ; tens = char(floor([1 :26]/10)+'0'); disp([tens; ones; letters]);
Formatted output
Sometimes you want to specify the output precisely. The fprintf() command allows you to specify a formatting string. fprintf(format_string, variables) will print the values in the variables as specified in the format_string. Places for numbers in the format string are specified like: %-12.5e %{+,-,0}{field width}.{precision}{conversion} +: include sign, -: left justify, 0: pad with zeros
Formatted output
Conversion characters:
%c %d %e %E %f %g %G %s %u
single character decimal number exponential notation (lowercase e) exponential notation (uppercase E) fixed point notation the more compact of %e or %f the more compact of %E or %f string decimal (unsigned)
Formatted output
Special characters in the format string
\t \n
\\ \%
tab new line backslash percent
fprintf()
Example:
num = 1234.56789; fprintf(`The number is %f !',num);
Output:
The number is 1234.56789 !
fprintf()
Example:
num = 1234.56789; fprintf(`The number is %e !',num);
Output:
The is number 1.2345678e+003 !
fprintf()
Example:
num = 1234.56789; fprintf(`The number is %g !',num);
Output:
The number is 1234.567 !
fprintf()
Example:
num = 1234.56789; fprintf(`The number is %.1f !',num);
Output:
The number is 1234.6 !
fprintf()
Example:
num = 1234.56789; fprintf(`The number is %08.1f !',num);
Output:
The number is 001234.6 !
Exercise 2
Which program, given a list of inventory item names (prod) and a list of the quantity and price will print a list in the format:
item hammer nails saw quantity 20 2000 5 price 12.50 0.10 25.00
Exercise 2
Which program, given a list of inventory item names (prod) and a list of the quantity and price will print a list in the format:
item hammer nails saw quantity 20 2000 5 price 12.50 0.10 25.00
2. fprintf('%-10s%10s%10s\n', 'item', 'quantity', 'price'); for n = 1:length(quant) fprintf('%-10s%10d%10.2f\n',prod(n,:),quant(n),price(n)); end
Save/Load
Sometimes during a MATLAB session or in the course of executing an M-File program there are one or more matrices that have data you would like to save to use later possibly in a different context. save can be called with or without parentheses. If it is called with parentheses then each argument is a string.
save
Examples
save save()
What it does Save all workspace variables in a file called matlab.mat
save
Examples
save mydata.mat save(`mydata.mat')
What it does Save all workspace variables in a file called mydata.mat
save
Examples
save mydata.mat X Y save(`mydata.mat', `X', `Y')
What it does Save the data in X and Y in a file called mydata.mat
save
Examples save mydata.txt X Y -ascii save(`mydata.txt', `X', `Y', `-ascii')
What it does Save the data in X and Y in a file called mydata.txt in ASCII format. Note the default is a binary format that is not easily readable outside of MATLAB.
save
Examples save mydata.txt X* -ascii save(`mydata.txt', `X*', `-ascii') What it does Save the data in any matrix starting with an X in mydata.txt in ASCII format.
save
Examples save mydata.txt X* -ascii -double save(`mydata.txt', `X*', `-ascii -double') What it does Save the data in any matrix starting with an X in mydata.txt in 16 digit ASCII format. The default is 8 digits.
save
CAVEATS
Data must be 2D character or data array Imaginary part of complex numbers is lost
If using load to read data all items must
have the same number of columns All data is written as floating point numbers; there is no record of which were character and which were floating point.
Exercise 3
Which program will take in up to 4 string arguments and save the matrix with the name corresponding to each string in a .mat file with the same name? i.e. savevars(`this', `that') would save the matrix this in the file this.mat and the matrix that in the file that.mat
Exercise 3
1.
function savevars(v1,v2,v3,v4) if nargin > 3 & ~isempty(v4) save([v4 `.mat'],v4); end if nargin > 2 & ~isempty(v3) save([v3 `.mat'],v3); end if nargin >1 & ~isempty(v2) save([v2 `.mat'],v2); end if nargin > 0 & ~isempty(v1) save([v1 `.mat'],v1); end
load
Examples
load load()
What it does Load all workspace variables in a file called matlab.mat
load
Examples
load mydata.mat load(`mydata.mat')
What it does Load all workspace variables in a file called mydata.mat (Matlab assumes binary format)
load
Examples
load mydata.ext load(`mydata.ext')
What it does Load all workspace variables in a file called mydata.ext (If ext is anything but mat then Matlab assumes ASCII format)
load
Examples
load mydata.ext -mat load(`mydata.ext', `-mat')
What it does Load all workspace variables in a file called mydata.ext that is in binary format.
load
Examples
load mydata.mat -ascii load(`mydata.mat', `-ascii')
What it does Load all workspace variables in a file called mydata.mat that is in ASCII format.
load
Examples
load mydata.mat X load(`mydata.mat', `X')
What it does Load the matrix X from a file called mydata.mat
load
Examples
load mydata.mat X Y load(`mydata.mat', `X', `Y')
What it does Load the matrices X and Y from a file called mydata.mat
load
Examples
load mydata.mat X* load(`mydata.mat', `X*')
What it does Load the matrices that start with an X from a file called mydata.mat
General File I/O
There are also several commands provided to write to files on disk. To open a file: fid = fopen( filename, permission ); fid = fopen(`Myfile.txt', `r'); To close a file: close(fid)
Permissions
`r' `w' `a' `r+' `w+' `a+'
read only write to new file append to new or existing file read and write read and overwrite read and append
fprintf with files
You can use fprintf to output to files
fid = fopen(`Myfile.txt', `w'); fprintf(fid, `It is %.2g meters long', num);
fscanf
There is an analogous command called fscanf to get data fid = fopen(`Myfile.txt', `r'); decnum = fscanf(fid, `%d');
fread/fwrite
There are also commands for reading and writing binary data, but we will not detail them here.