1: read the data from the existed file

a: 

suppose that you have the file "bisection.txt", which contains 9 rows and 4 columns, 

fid = fopen('bisection.txt','r');
A = fscanf(fid,'%f',[9,4]);
fclose(fid);

b:

Suppose that you have the file "bisection" (no extension, 
note the difference with the case 'a'),

load bisection;

bisection will store all the data in the file "bisection";

2:

x = [2,2.5,4];
y = 1./x;
p = polyfit(x,y,2); % generate the coefficients of polynomial of degree 2  
x1 = linspace(2,4,100);
y1 = 1./x;
y2 = polyval(p,x1); % get the value at x1 with the function of polynomial
plot(x,y,'o',x1,y1,'k:',x1,y2,'b-'); 

3:

Symbol     color     symbol      Linestyle                   
y          yello       .           point
r          red        o            circle
g          green      -            solid line
b          blue       :            dotted line
w          white      -.           dash-dot line
k          black      --           dashed line 
