tutor1.m

很多matlab的源代码

% ADSP Toolbox: Version 2.0 
% For use with "Analog and Digital Signal Processing", 2nd Ed.
% Published by PWS Publishing Co.
%
% Ashok Ambardar, EE Dept. MTU, Houghton, MI 49931, USA
% http://www.ee.mtu/faculty/akambard.html
% e-mail: [e-mail]
% Copyright (c) 1998


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%                      MATLAB - A TUTORIAL INTRODUCTION


%MATLAB is an interactive and programmable matrix-manipulation program which 
%allows numerical evaluation of scientific problems  (entered  into  MATLAB 
%much the same way as they might be  on  paper).  This  extremely  powerful 
%program relies on a variety of numerically well behaved (and state of  the 
%art) routines for performing a large number  of  mathematical  operations. 

%The command prompt is the  symbol >>. A list  of available functions and 
%commands may  be displayed by typing  "help"  (all  commands 
%are to be followed by enter, of course). To list a brief description of  a 
%specific command, type "help" followed by the name of the command

%To get help on the function tan we type
help tan

pause  %strike a key to continue

%GETTING OUT OF MATLAB
%Typing  either "exit" or "quit" at the command prompt will get you out of 
%the program  and back to the operating system (e.g. DOS).

%AN IMPORTANT NOTE
%MATLAB is normally case-sensitive.All built-in commands are in lower  case. 

%The commands "casesen off" or "casesen on"  make  it  case  insensitive  or 
%otherwise.

%THE BASICS
%Let us now begin at the beginning by explaining how to  enter  commands.
%A knowledge of the simple operations "+, -, *, /" used by MATLAB to denote 
%the usual operations of addition, subtraction, multiplication and  division 
%are all we shall need for the moment.(we shall  have  more  to  say  about 
%their quirks later, of course).

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%Consider the MATLAB command 
%sin(0.25*pi)

%Note that (a)"pi" is a built in constant, (b) "sin" is  the  built  in 
%function that returns the sine of an angle, (c) angles are  accepted  (and 
%returned) in radians and not degrees and (d) numbers  can  be  entered  in 
%almost any format such as 0.25, 1/4 or 2.5e-1.

%On pressing the ENTER key this command is instantly executed, as  is  every 
%other command "entered" at the command prompt, and MATLAB responds with the 
%on-screen display
%ans
%= 0.7071

sin(0.25*pi)
%This result corresponds to sin(45 deg). Even though it is displayed to four 
%digit accuracy, MATLAB actually performs all numeric computations in double 
%precision. Results can be displayed in different formats. More on that later.

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%Getting back to the answer, note  that  it  is  stored  in  the 
%variable "ans", since no variable was specified on the  command  line.  One 
%way to assign the result to a variable s say, is as follows

%s=ans
%This will result in the display
%s
%= 0.7071
s=ans
%Or we may enter the following
s=sin(pi/4)
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%You can use any legal variable names, even "pi" if you wish e.g. pi=s

%But if you do, remember that user defined variables  take  precedence  over 
%those used within MATLAB. Be warned  that  "pi"  will  no  longer  perform
%the  function intended by MATLAB but represent the value assigned to it by s
%until you clear it from memory by issuing the command "clear pi" from the
%command prompt This restores the intended default to the variable "pi"
%It is poor practice to use variable names already reserved by MATLAB.
%Upon execution of a command, MATLAB always returns with  the command prompt

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%The variable "ans" can, of course, be manipulated like  any other variable
%Consider the following statements

exp(-1)    %The exponential quantity e^(-1)
ans*exp(1)   %Ans here is e^(-1) so this should yield 1
ans*2        %Ans here is 1, so this should yield 2
%NOTES: 1.The variable "ans" always stores results of the most recent command.
%2.Comments may be inserted with any command following the percent sign  "%" 
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%FORMAT
%MATLAB displays results in short format even though all results are stored
%in double precision

%To see all subsequent results in in double precision scientific, use
format long e

%If we now display the variable s which equals sin(pi/4), it will result in
s

%To revert to the default format, use
format
s
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%ARRAYS OR ROW VECTORS
%Arrays or rows of values can be generated by entering values  separated  by 
%commas or spaces and enclosed in square brackets. The statement
x=[1 3 5 7] %stores the numbers 1 3 5 7 in the variable x
%THE ELLIPSIS
%An array list longer than one line can be continued on  the  next by using
%an ellipsis (... i.e. two or  more  periods followed by a carriage return)
%No MATLAB prompt or display will appear until the  enter key is pressed
%again. In the following command, the first line contains an ellipsis followed
%by a carriage return. The second line is also followed by a carriage return
%Only after the second line is entered is the command executed
x=[1  2  3  4 ...
5  6]
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%THE COLON
%Generation of arrays is made painless using the colon ":". Thus
x=1:6

%yields the array [1  2  3  4  5  6]

%The default increment is one. For a different increment, use for example
y=0.2:.2:1.1
%yields the array [.2 .4 .6 .8 1.0]
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%THE SEMI-COLON
%The semi-colon ";", used after a command is equally useful.  It  actually 
%suppresses the on-screen display of results (but not the  execution  of  a 
%command). Thus the command z=1:300; generates an array with values from 1 
%to 300 and simply returns to  the  MATLAB  prompt  upon  execution  without 
%displaying the values on the screen. The result is

z=1:300;
%The variable z does indeed exist in the workspace. For example

z(1)  %the first element of the array z which should equal 1

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%ABORTING DISPLAYS OR EXECUTION
%Clearly, for large matrices it could get tiresome to wait  for  the  entire 
%array to be displayed if the semi-colon is not used. If you forget and want
%to abort the display of a variable, typing "CTRL-C" (typing C while 
%holding the CTRL key pressed) returns you to  the  MATLAB  prompt  without 
%affecting  the  variable  whose  values  were  being  displayed.

%Actually,  typing"CTRL-C"  aborts  the  currently  executing   command   or 
%operation and is therefore also very  useful  if  you  want  to  abort  and 
%terminate an unintended command if it has not been already executed 

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%THE COMMA, SEMI-COLON AND CONCATENATION
%More that one command can  be  included  in  a  single  line  provided  the 
%commands are separated by commas (which  do  not  suppress  the  on-screen 
%display of the preceding command) or semi-colons (which do).

x=2,y=3*x*x;z=y-6*x  %This will display x and z but not y
%Note that the semi-colon suppresses display of the  second  command 

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%VARIABLES AND MATRICES
%Every variable in MATLAB is regarded as a matrix , even if  its  dimensions 
%are 1*1 (a single elemen). No  dimensioning  (or  type  declaration)  is 
%required and MATLAB automatically allocates the appropriate storage.  Index 
%values for matrices always start  at  one  (and  not  zero  as  with  some 
%computer languages). Individual elements are addressed by  their  row  and 
%column indices (as in A(2,3), the element in row 2 and column 3). If  you 
%execute the following statement

avar(2,2)=3
%Notice how MATLAB has recognized a(2,2) as the  element  of  a  matrix  and 
%assigned enough storage to avar which it recognizes as a  2*2  matrix.  Now 
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%if we enter
avar(2,3)=4
%storage is automatically allocated to avar based on the  element  of 
%avar that is encountered.
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%Element values can be changed. For example
avar(1,2)=5
%Elements of a matrix may be entered by rows,  with  elements  separated  by 
%spaces (or commas) and rows separated by  semi-colons,  all  within  square 
%brackets. The command

b=[1 2 4; 3 1 2]   %results in a 3x2 matrix

%NOTE: In this format, all rows must have the same number of elements.

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%THE COLON AGAIN
%A colon is used to denote an entire range of values.  For  example,  A(2,3) 
%denotes one element of matrix A while A(2,:) denotes the entire second  row 
%of A, regardless of how many columns there are. Enter the command

c=b(2,:) %assigns the entire 2nd row of b to the variable c
%Similarly

b(:,3)     %denotes the entire third column of b

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