Without using the roots command, write a function to calculate roots of the quadratic equation

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Chris
Chris 2013-6-24
Without using the roots command, write a function to calculate roots of the quadratic equation
ax^2+bx+c=0
Inputs to the function should be the coefficients a, b and c and output should be the roots. Test your program by setting a=2,b=3,c=-1
can someone help me out with this? I cant think of anything but roots to use. would I have to use poly? or fzero?

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Evan
Evan 2013-6-24
No need to call any built-in function. Just write your own using the quadratic formula.

更多回答（2 个）

Tom
Tom 2013-6-24
I'd recommend maths.
James Tursa
James Tursa 2013-6-24
You can use one of the formulations here:
http://en.wikipedia.org/wiki/Quadratic_equation
The quadratic formula is listed, of course, but that is prone to cancellation error. So I would advise impressing your professor by coding up the algorithm under the "Avoiding loss of significance" section.
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Chris
Chris 2013-6-24
This confuses me still how do I add in an Algorithm? Im terrible at this matlab stuff. so would i have to put the original function in?
James Tursa
James Tursa 2013-6-25
It would be best if you could post what you have so far and then we can comment on it and suggest improvements. E.g., a function outline would be this (e.g., put in a file called quadratic_roots.m):
function [x1 x2] = quadratic_roots(a,b,c)
% add your code here to calculate x1 and x2
return
end

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