whats wrong in the code may someone help me to get same answer as the example

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Mohamad Yousif Al Ayoubi
评论： Walter Roberson 2017-6-29
Write the function find_zero that is defined like this function
x = find_zero(f,x1,x2)
The first input argument is special. It is a “function handle”. A function handle is gotten by typing @ and the name of any function. For example,
x = find_zero(@sin,-1,1)
will give f the function handle for MATLAB’s built-in sin function. Then, inside find_zero, the statement
y = f(-1)
would set
y = sin(-1)
Note that the @ sign is not used inside the function. Only the caller uses it. All other arguments to find_zero are scalar numbers, and x1 is less than x2. The goal of the function is to find an x that lies in the range from x1 to x2 such that after the command, y = f(x), is executed inside the function find_zero, y is approximately zero as defined by abs(y) < 1e-10. All you know about the function f is that it has one scalar input and one scalar output, and a plot of its values crosses the x-axis exactly once between x1 and x2, as, for example, in the figure 3. It is the responsibility of the caller to call the function with arguments that obey these rules.
Figure 3 Output plot for x1 and x2 (Hint: Remember to label your axis’s) Here are two sample runs:
>> find_zero(@sin,-2.5,2.3) % as shown in the figure
ans =
-6.4000e-11//
>> format long
//>> find_zero(@cos,-2,1.3)
ans =
-1.570796326871000
in the function:
>> function x = find_zero(f,x1,x2) % Function definition
>> y = f(x2); % Computing the function value at x = x2
>> while abs(y) > 1e-10 % exit loop if y approximatly equal to zero
>> x=x2-y*(x2-x1)/(y-f(x1)); % finding new x using secant method
>> x1=x2;%copy the value of x2 to x1
>> x2=x;% copy the value of x to x2
>> y = f(x2); % Computing the function value at new x
>> end % End of loop
>> end % End of program

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回答（3 个）

Harsh
Harsh 2017-5-11
If you still need help with this, please contact MathWorks Technical Support here: https://www.mathworks.com/support/contact_us/
Please be sure to provide a detailed description of the exact issue and attach any relevant files / code / examples required to investigate the issue.
Walter Roberson
Walter Roberson 2017-5-11
It is not permitted to define functions at the command prompt. You need to store the code for your function inside a file named find_zero.m
  2 个评论
Steven Lord
Steven Lord 2017-5-15
MATLAB does not allow you to define functions like that at the prompt in the Command Window. [This work is too complicated to write as an anonymous function, at least not without some rather creating and advanced techniques.]
If you want to define a function (like your assignment requires you to do) you must define it in a function file like Walter said.

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Ganesh Prasad B K
Ganesh Prasad B K 2017-6-29
Here is the code. Have a look at it
function x = find_zero(f,x1,x2)
tolerance = 1e-10;
if(f(x1)==0)
x=x1;
return
elseif(f(x2)==0)
x=x2;
return
else
while tolerance < abs((x2-x1)/2)
x3= mean([x1,x2]);
if(f(x3)==0)
x=x3;
return
elseif(f(x1)*f(x3)>0)
x1=x3;
elseif(f(x1)*f(x3)<0)
x2=x3;
end
x = x3;
end
end
end
  1 个评论
Walter Roberson
Walter Roberson 2017-6-29
I notice this code does not check that f(x1) and f(x2) are opposite sign. Using bisection like this is only valid if you know two points where the sign differs.

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