# Coding a function to find zeros using a variant of the bisection/secant method

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Lavorizia Vaughn on 28 Sep 2021
Commented: Walter Roberson on 29 Sep 2021
Hello, I have a programming assignment where I have to implement a matlab function that is a variant of the bisection and secant method. Please see attachment for exact details. I am having problems with the code. Will someone help me with the necessary fixes? My code is as follows: —————————————————————————————————————-
if true
% code
function p = bisection(f, a, b, tol)
w=1;
for i=1:100
p= a +(w*f(a)*(a-b)/f(b)-w*f(a));
fprintf(a,b,p,f(p));
if f(p)*f(b)>0
w=0.5;
else
w=1;
a=b;
end
b=p;
if abs(b-a)<tol
abs(f(p))<tol
break;
end
end.

Walter Roberson on 28 Sep 2021
No, no error about needing to use () . However,
output = bisection(@(x) sin(x)+3*cos(x).^2, -pi/2, pi/2, 1e-5)
Error using fprintf
Invalid file identifier. Use fopen to generate a valid file identifier.

Error in solution>bisection (line 7)
fprintf(a,b,p,f(p));
function p = bisection(f, a, b, tol)
w=1;
for i=1:100
p= a +(w*f(a)*(a-b)/f(b)-w*f(a));
fprintf(a,b,p,f(p));
if f(p)*f(b)>0
w=0.5;
else
w=1;
a=b;
end
b=p;
if abs(b-a)<tol
abs(f(p))<tol
break;
end
end
end
This is because the first parameter to fprintf must be one of:
1. A file identifier
2. A format character vector or format string scalar
3. A device object for some kinds of devices such as serialport objects
The first parameter you are passing is a, which is numeric but is not a valid file identifier.
Walter Roberson on 29 Sep 2021
fprintf('Lovorizia, the value for a was %g .\nAnd b was %g .\n, Then there was p, which was %g .\n And lastly, if you still care, f(p) was %g .\n', a, b, p, f(p));