0 个投票

I used a code for bisection method, which supposed to be working, unfortunately it´s not and I do not know what is the problem. This code also includes user defined precision and a counter for number of iterations. The error I´m getting is for the last line in the code: Undefined function or variable 'c'.
a=-5;
b=0;
tol = input('What precision would you like? ','s')
fa=a^3-20+exp(a);
fb=b^3-20+exp(b);
counter=1
while abs(b-a) > tol
c=(a+b)/2;
fx = c*c-2;
if fa*fc<0
b=c;
fb=fc;
elseif fb*fc<0
a=c;
fa=fc;
else
break
end
fprintf('Just finished iteration #%d\n', counter);
counter=counter+1;
end
x=c;

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John D'Errico
John D'Errico 2017-10-22

1 个投票

NEVER hard code a function. Outside of the loop, you appear to be tring to solve the function
x^3 - 20 + exp(x) == 0
Inside of the loop, you are trying to solve the problem
x^2 - 2 == 0
So even if this ever somehow incorrectly did terminate, you would get garbage for a result.
Learn how to use a function handle. Or learn how to define a function.
The real reason why your code failed? I think you don't understand how to use input. READ THE HELP!
tol = input('What precision would you like? ','s')
What precision would you like? 0.001
tol =
'0.001'
So I provided a tolerance of 0.001. But did MATLAB understand me? Because when you used input, you told MATLAB to accept the result as a string!
whos tol
Name Size Bytes Class Attributes
tol 1x5 10 char
So tol is the character string '0.001'. tol s NOT a number. Is there a good reason why you used input in that way? NO.
READ THE HELP FOR TOL.
help tol

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