x = linspace(-1/2,1/2,5)

x =

  Columns 1 through 4

  -0.500000000000000  -0.250000000000000                   0   0.250000000000000

  Column 5

   0.500000000000000

x = linspace(-1/2,1/2,100);
plot(x,sin(x),x,x);
plot(x,sin(x)-x);
1/8

ans =

   0.125000000000000

plot(x,sin(x)-x,x,1/2*x*x,x,-1/2 *x*x);
{Error using <a href="matlab:matlab.internal.language.introspective.errorDocCallback('mtimes')" style="font-weight:bold"> * </a>
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first
matrix matches the number of rows in the second matrix. To perform elementwise multiplication,
use '.*'.
} 
plot(x,sin(x)-x,x,1/2*x.*x,x,-1/2 *x.*x);
diary