Why is there an error when I called the function inputting the points

"Undefined function 'f' for input arguments of type 'double'.

Error in linearinterp>refine (line 11) if abs((f(x1)+f(x2))/2-f(xm))<tol

Error in linearinterp (line 3) points = refine(0, 7, 0.6);"

function linearinterp

f = @(x) (exp(-x/2).*sin(x.^2+8));

points = refine(0, 7, 0.6);

plot(points, f(points), 'r+');

hold on

plot(points, f(points));

hold off

end

function points = refine(x1, x2, tol)

xm = (x1+x2)/2;

if abs((f(x1)+f(x2))/2-f(xm))<tol

points=[x1,x2];

else

left=refine(x1, xm, tol);

right=refine(xm, x2, tol);

points=[left, right(2:length(right))];

end

end

Answer 1

[Mischa Kim]

Ehi, you need to define function f again in refine() to make it work. In other words:

function points = refine(x1, x2, tol)
f = @(x) (exp(-x/2).*sin(x.^2+8));
...

Reason begin, f is only in scope of linearinterp(). It is not in scope for refine() and therefore unknown. Alternatively, you can pass f as an input argument to refine():

points = refine(0, 7, 0.6, f)

...

function points = refine(x1, x2, tol, f)

In that case you do not need to define f again.