>> n=5

n =

     5

>> h=1/n;
>> x=0:h:1

x =

         0    0.2000    0.4000    0.6000    0.8000    1.0000

>> help diag


>> A=diag(ones(n-2,1),-1)

A =

     0     0     0     0
     1     0     0     0
     0     1     0     0
     0     0     1     0


>> A=diag(ones(n-2,1),-1)-2*diag(ones(n-1,1),0)+diag(ones(n-2,1),1)

A =

    -2     1     0     0
     1    -2     1     0
     0     1    -2     1
     0     0     1    -2

>> u=h^2*(A\sin(pi*x(2:n)'))

u =

   -0.0616
   -0.0996
   -0.0996
   -0.0616

>> plot(x(2:n),u,'r-o',x,-sin(pi*x)/pi^2,'k-^')
>>