MATLAB: If condition not working, any ideas why

bisection methodif statement

%
x=0:0.1:2;
y=12*x.^2+10*x-28;%f(x)
t=-13*x.^2+15*x+28;%g(x)
h=25*x.^2-5*x-56;
plot(x,y,'r',x,t,x,h,'b')
title('intersection point') 
xlabel('x-axis')
ylabel('y-axis')
grid on
disp('Initial guesses') %Input for interval one
a=input('first guess: ');
b=input('Second guess: ');
func = @(x) 25*x^2-5*x-56; % f(x)-g(x) = 25*X^2-5*X-56
%----bisection method
for i=1:1000                         
c=(a+b)/2; 
Fc=func(c);
Fb=func(b); 
if(Fc*Fb>0) 
b=c; 
else
a=c; 
end 
end
disp(c)
funcy = @(x) 12*x^2+10*x-28;
funcg = @(x)-13*x^2+15*x+28;
%y1 = funcy(c);
if funcy(c)== funcg(c)    
disp('intersection point')  % First intersection point
disp('X:')
disp(c)
%disp('Y:')
%disp(y1)
%hold on   
%plot(c,y1,'ro') 
else
  disp('no')   
end
This is the code for the bisection method, the part of the bisection method is working perfectly fine, it displays the value of the intersection, but when i put the condition: if funcy(c)== funcg(c) (which in the calculator it gives me the same answer: 18.72) it displays the else option. I have also tried to change the condition but still the same problem. Thank you for your attention.

Best Answer

To compare floating point numbers, you need to use a tolerance. See the FAQ: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F
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