is there a problem with my operators???

EDU>> refine(0, 7, .1) Undefined function 'f' for input arguments of type 'double'.

Error in refine (line 3)
if abs((f(x1)+f(x2))/2-f(xm))<tol

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

function linearinterp
x=linspace(-5, 2*pi, 30);
y=exp.^(-x./2).*sin(x^.2+8);
points=refine(0, 7, 0.1);
plot(x, y, points, f(points), 'r+');
hold on
plot(points, f(points));
hold off
end

Answer 1

[Azzi Abdelmalek]

What is f in your function refine?

[Ehi Eromosele]

the formula for Bisection. f is the y function.

[Azzi Abdelmalek]

And what is the y function?

[Ehi Eromosele]

the function i'm trying to interpolate and plot. on the interval 0 and 7 with tolerance 0.7

[Azzi Abdelmalek]

Ehi, look at the first three lines of your function refine

function points=refine(x1, x2, tol)
xm = (x1+x2)/2;
if abs((f(x1)+f(x2))/2-f(xm))<tol

In the third line f(x1) is used. How Matlab is supposed to know what f represent?

[Ehi Eromosele]

o so instead f input y(x1)+y(x2)/2-y(xm)<tol

[Ehi Eromosele]

instead of f

[Azzi Abdelmalek]

What is the difference? y is also unknown

[Ehi Eromosele]

I wanted the function refine to receives the points and uses it to decide when to subdivide intervals. Then y helps plot the function when the points are implemented.

[Azzi Abdelmalek]

I am not sure if you know how functions work. Look at this simple example:

function out=example(in1,in2,in3)
out=(in1+in2+in3)/3

Save this file as example.m

In Matlab windows command, you can call the function example by providing the values for in1, in2 and in3

m=Example(10,45,25)

[Ehi Eromosele]

Wait azzi what if I did like this.

[Ehi Eromosele]

function linearinterp
x=linspace(-5, 2*pi, 30);
y=exp.^(-x./2).*sin(x.^2+8);
points=refine(0, 7, 0.1);
plot(x, y, points, f(points), 'r+');
hold on
plot(points, f(points));
hold off
end
function points=refine(x1, x2, tol)
xm = (x1+x2)/2;
y=f(x);
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

[Ehi Eromosele]

i'll post it for better view...