MATLAB HINTS - HOMEWORK 1
M. Nelson  Spring 2004

New Matlab Commands
(to get more info, type 'help <cmd>' at the matlab prompt)
arrays
 a(i) is the ith element of a vector;
a(i,j) is element (i,j) of a 2-D matrix
Matlab matrices can have more than 2 dimensions.
Matlab indexing is 1-based, not 0-based like some other languages, so
  the first element is a(1), not a(0).
axis In HW0 we discovered that
axis([xmin xmax ymin ymax]) sets scaling for the x- and y-axes.

Here we show some addition things the 'axis' command can do:
axis equal  sets the aspect ratio so that equal tick mark
       increments on the x-,y- and z-axis are equal in size.
axis square  makes the current axis box square in size.
axis normal  restores the current axis box to full size and
        removes any restrictions on the scaling of the units.
        This undoes the effects of  axis square and axis equal.
axis off  turns off all axis labeling, tick marks and background.
axis on  turns axis labeling, tick marks and background back on.
 
fix
 fix(x) rounds x to the nearest integer towards zero.
See also floor, round, ceil
for/end
 repeat statements a specific number of times
for i = 1:N
    a(i) = sqrt(i);
end
if/else/end
 The general form of the if statement is

if  expression
         statements
elseif  expression
         statements
else
         statements
end
 
The statements are executed if the real part of the expression has all non-zero elements. The else and elseif parts are optional. The expressions oftent contain relational operators, such as <, <=, >, >=, ==, and ~=.
See also relop.
 
length
 length(x) returns the length of vector x.  It is equivalent to max(size(x)) for non-empty arrays and 0 for empty ones.
max
 For vectors, max(x)  is the largest element in x
For matrices, max(x) is a row vector containing the maximum element from each column of x.
min
 For vectors, min(x)  is the smallest element in x
For matrices, min(x) is a row vector containing the minimum element from each column of x.
num2str
 txt = num2str(x) converts the variable x into a string representation txt
with about 4 digits and an exponent if required.  This is useful for
labeling plots with the title, xlabel, ylabel and text commands.
rand
 Uniformly distributed random numbers on the interval (0.0,1.0).
rand is a single random number
rand(m,1)  is an m-by-1 column vector with m random entries
rand(m,n)  is an m-by-n matrix with m x n random entries.

rand('state',0)  resets the generator to its initial state.
relop
 relational operators
<
 less than
<=
 less than or equal to
>
 greater than
>=
 greater than or equal to
==
 equal to
~=
 not equal
&
 logical AND
|
 logical OR
~
 logical NOT

Example:
if ( (v(i) > thresh) & (t >= tstart) & (t < tstop) )
    statements
end
size
 [m, n] = size(x)  for vector/matrix x, returns the number of rows m and columns n as separate output variables.
d = size(x) returns the size as a two-element vector d = [m, m] 
text
 text(x, y, 'string') adds the text in the quotes to location (x,y) on the current axes, where (x,y) is in units from the current plot. 
who
 who lists the variables in the current workspace
 
whos
 lists more information about each variable, including size

Example Script
(you can copy-and-paste this into the matlab command window or save it as an m-file)
clear;
figure(1);
clf;

% number of points
NPT = 6;

% generate random (x,y) coordinates
rand('state',0);
x = rand(NPT,1);
y = rand(NPT,1);

% plot the points
plot(x, y,'ro-'); hold on;

% add labels
for ipt= 1:NPT
    myString = ['Point ' num2str(ipt)];
    text(x(ipt)+.02 , y(ipt)+.02, myString);
end

% set the axis limits
axis([0 1 0 1]);
grid on;
axis equal;