m=4,x=linspace(0,1,m)';

m =

     4

x

x =

         0
    0.3333
    0.6667
    1.0000

h=diff(x)

h =

    0.3333
    0.3333
    0.3333

1./(h(1:m-2)+h(2:m-1))

ans =

    1.5000
    1.5000

d=1./(h(1:m-2)+h(2:m-1))

d =

    1.5000
    1.5000

spdiags([[-d;0;0],[0;0;d]],[-1,1],4,4)

ans =

   (2,1)      -1.5000
   (3,2)      -1.5000
   (2,3)       1.5000
   (3,4)       1.5000

full(spdiags([[-d;0;0],[0;0;d]],[-1,1],4,4))

ans =

         0         0         0         0
   -1.5000         0    1.5000         0
         0   -1.5000         0    1.5000
         0         0         0         0

toeplitz([0,-1,0,0],[0,1,0,0])

ans =

     0     1     0     0
    -1     0     1     0
     0    -1     0     1
     0     0    -1     0

h=0.3

h =

    0.3000

toeplitz([0,-1/(2*h),0,0],[0,1/(2*h),0,0])

ans =

         0    1.6667         0         0
   -1.6667         0    1.6667         0
         0   -1.6667         0    1.6667
         0         0   -1.6667         0

toeplitz(sparse([0,-1/(2*h),0,0]),sparse([0,1/(2*h),0,0]))

ans =

   (2,1)      -1.6667
   (1,2)       1.6667
   (3,2)      -1.6667
   (2,3)       1.6667
   (4,3)      -1.6667
   (3,4)       1.6667

toeplitz([-2,1,0,0])

ans =

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

y=@(x) sin(x)

y = 

    @(x)sin(x)

x=[0,1]

x =

     0     1

u=y(x)+1e-4

u =

    0.0001    0.8416

y(x)-u

ans =

   1.0e-04 *

   -1.0000   -1.0000

xx=linspace(0,1,100);
uu=y(x)+1e-5;
norm(y(x)-u)

ans =

   1.4142e-04

norm(y(xx)-uu)
??? Error using ==> minus
Matrix dimensions must agree.

uu=y(xx)+1e-5;
norm(y(xx)-uu)

ans =

   1.0000e-04

norm(y(x)-u,inf)

ans =

   1.0000e-04

norm(y(xx)-uu,inf)

ans =

   1.0000e-05

diary off