Applied Numerical Methods Using MATLAB. Won Y. Yang
Читать онлайн.| Название | Applied Numerical Methods Using MATLAB |
|---|---|
| Автор произведения | Won Y. Yang |
| Жанр | Математика |
| Серия | |
| Издательство | Математика |
| Год выпуска | 0 |
| isbn | 9781119626824 |
>lookfor repeat or >help for
to find the MATLAB commands in connection with ‘repeat’ or to find information about the ‘for loop’
1.1.1 Input/Output of Data from MATLAB Command Window
MATLAB remembers all input data in a session (anything entered through direct keyboard input or running a script file) until the command ‘ clear()’ is given or you exit MATLAB.
One of the many features of MATLAB is that it enables us to deal with the vectors/matrices in the same way as scalars. For instance, to input the matrices/vectors,
type the following statements in the MATLAB Command window:
>A=[1 2 3;4 5 6] A= 1 2 3 4 5 6 >B=[3;-2;1]; %put the semicolon at the end of the statement to suppress the result printout onto the screen >C=[1 -2 3 -4]
At the end of the statement, press <Enter> key if you want to check the result of executing the statement immediately. Otherwise, type a semicolon ‘;’ before pressing <Enter> key so that the Command window will not be overloaded by a long display of results.
1.1.2 Input/Output of Data Through Files
MATLAB can handle two types of data files. One is the binary format mat‐files named ***.mat. This kind of files can preserve the values of more than one variable, but will be handled only in the MATLAB environment and cannot be shared with other programming environments. The other is the ASCII dat‐files named ***.txt, which can be shared with other programming environments, but preserve the values of only one variable.
Beneath are a few sample statements for storing some data into a mat‐file in the current directory and reading the data back from the mat‐file.
>save ABC A B C %store the values of A,B,C into the file 'ABC.mat' >clear A C %clear the memory of MATLAB about A,C >A %what is the value of A? Undefined function or variable 'A' >load ABC A C %read the values of A,C from the file 'ABC.mat' >A % the value of A A= 1 2 3 4 5 6
If you want to store the data into an ASCII dat‐file (in the current directory), make the filename the same as the name of the data and type ‘ ‐ascii’ at the end of the save statement.
>save B.txt B -ascii
However, with the save/load commands into/from a dat‐file, the value of only one variable having the lowercase name can be saved/loaded, a scalar or a vector/matrix. Besides, nonnumeric data cannot be handled by using a dat‐file. If you save a string data into a dat‐file, its ASCII code will be saved. If a dat‐file is constructed to have a data matrix in other environments than MATLAB, every line (row) of the file must have the same number of columns. If you want to read the data from the dat‐file in MATLAB, just type the (lowercase) filename ***.txt after ‘ load’, which will also be recognized as the name of the data contained in the dat‐file.
>load b.txt %read the value of variable b from the ascii file 'b.txt'
At the MATLAB prompt, you can type ‘nm112’ (the filename excluding the extension name part “.m”) and <Enter> key to run the following M‐file “nm112.m” consisting of several file input(save)/output(load) statements. Then you will see the effects of the individual statements from the running results appearing on the screen.
%nm112.m clear A=[1 2 3;4 5 6] B=[3;-2;1]; C(2)=2; C(4)=4 disp('Press any key to see the input/output through Files') save ABC A B C %save A,B & C as a MAT-file named 'ABC.mat' clear('A','C') %remove the memory about A and C load ABC A C %read MAT-file to recollect the memory about A and C save B.txt B -ascii %save B as an ASCII-file file named 'b.txt' clear B load b.txt %read ASCII-file to recollect the memory about b b x=input('Enter x:') format short e x format rat, x format long, x format short, x
1.1.3 Input/Output of Data Using Keyboard
The command ‘ input’ enables the user to input some data via the keyboard. For example,
>x=input('Enter x: ') Enter x: 1/3 x= 0.3333
Note that the fraction 1/3 is a nonterminating decimal number, but only four digits after the decimal point is displayed as the result of executing the above command. This is a choice of formatting in MATLAB. One may choose to display more decimal places by using the command ‘ format’, which can make a fraction show up as a fraction, as a decimal number with more digits, or even in an exponential form of a normalized number times 10 to the power of some integer. For instance:
>format rat % as a rational number >x x= 1/3 >format long % as a decimal number with 14 digits >x x= 0.33333333333333 >format long e % as a long exponential form >x x= 3.333333333333333e-001 >format hex % as a hexadecimal form as represented/stored in memory >x x= 3fd5555555555555 >format short e % as a short exponential form >x x= 3.3333e-001 >format short % back to a short form(default) >x x= 0.3333
Note that the number of displayed digits is not the actual number of significant digits of the value stored in computer memory. This point will be made clear in Section 1.2.1.
There are other ways of displaying the value of a variable and a string on the screen than typing the name of the variable. Two useful commands are ‘ disp()’ and ‘ fprintf()’. The former displays the value of a variable or a string without ‘ x=’ or ‘ ans=’; the latter displays the values of several variables in a specified format and with explanatory/cosmetic strings. For example:
>disp('The value of x='), disp(x) The value of x= 0.3333
Table 1.1 summarizes the type specifiers and special characters that are used in ‘ fprintf()’ statements.
Table 1.1 Conversion type specifiers and special characters used in fprintf() statements.
| Type specifier | Printing form: fprintf(‘**format string**’,variables_to_be_printed,..) | Special character | Meaning |
%c
|
character type |
\n
|
new line |
%s
|
string type |
\t
|
tab |
%d
|
decimal integer number type |
\b
|
backspace |
%f
|
floating point number type |
\r
|
CR return |
%e
|
decimal exponential type |
\f
|
form feed |