Help with a vector

Hello. I have come up with the following code:

function p = findmanyzeros(f, a, b, n, tol)
x = a + (b-a)*(0:n)/n;
fx = f(x);
p = [];
for i = 1:n
    if sign(fx(i)) ~= sign(fx(i+1))
        p(end+1) = findzero(f, x(i), x(i+1), tol);
    end
end

My instructions were to Implement a MATLAB function findmanyzeros of the form function p=findmanyzeros(f, a, b, n, tol)

which finds zeros in the interval [a, b] using the following strategy:

1. Compute n+1 equidistant points xk, k=0,...,n, between a and b

2. For k = 1,...,n, if f(xk) and f(xk−1) have different signs, compute a zero using findzero

3. The output vector p should contain all the computed zeros

[Cris LaPierre]

Sorry if I missed it, but what is your question?

[Lavorizia Vaughn]

its not working. i keep getting that there is an error on

p(end+1) = findzero(f, x(i), x(i+1), tol);

[Jan]

Whenever you mention an error in the forum, post a copy of the complete error message. It is much easier to solve an error that to guess, what the error is.

[Lavorizia Vaughn]

>> f= @(x) cos(x)-x;

>> findzeros(f, 0, 1, 10, 10^-4)

Unrecognized function or variable 'fx'.

Error in findzeros (line 6)

if sign(fx(i)) ~= sign(fx(i+1))

>>

[Lavorizia Vaughn]

f= @(x) cos(x)-x

f = function_handle with value:
    @(x)cos(x)-x

findzeros(f, 0, 1, 10, 10^-4)

Unrecognized function or variable 'fx'.

Error in solution>findzeros (line 7)
if sign(fx(i)) ~= sign(fx(i+1))

function p = findzeros(f,a,b,n,tol)
x=a+(b-a)*(0:n)/n;
p=[];
for i = 1:n
    if sign(fx(i)) ~= sign(fx(i+1))
        p(end+1) = findzero(f, x(i), x(i+1), tol);        
    end
end
end

Answer 1

[Cris LaPierre]

You have not defined a variable fx inside your findzeros function. Do you mean to use f?

You have created a recursive function but you have not defined an exit criteria. Since sign(f(i) always is the same as sign(f(i+1)), p is never assigned a value, and your result is an empty vector.

f= @(x) cos(x)-x;
f(1:10)

ans = 1×10

-0.4597 -2.4161 -3.9900 -4.6536 -4.7163 -5.0398 -6.2461 -8.1455 -9.9111 -10.8391

[Lavorizia Vaughn]

thank you ive figured it out.