I am trying to plot, at x=pi/4, the variation of the error percentage along h (h increments from 0.01 to 0.5), using the first order central difference method for function f(x)=sinx. Can't figure out what's wrong with the code. Any help please?

z = cos(pi/4);%Exact value

n=0;

for h=0.01:0.01:0.5;

    n=n+1;
   t(n) =((sin(pi/4)+(h))-(sin(pi/4)-(h)))/(2*h);
    Percent_Error(n)= abs (((t(n)-(z))./z)*100);

end

hold on

plot (t, Percent_Error);

Answer 1

[Roger Stafford]

What you want for t(n) is:

 t(n) =(sin(pi/4+h)-sin(pi/4-h))/(2*h);

In other words the increment 'h' should be applied to the argument of the sine function, not outside it.