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?

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MF
MF 2016-1-5
编辑： Roger Stafford 2016-1-5
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);

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回答（1 个）

Roger Stafford
Roger Stafford 2016-1-5
编辑：Roger Stafford 2016-1-5
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.

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