how to write a function for quadratic equation

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Alisha Mistry
Alisha Mistry 2019-12-6
评论： Steven Lord 2024-7-13
I wrote this into matlab but it doesn't work, can someone explain why?
function [x1,x2] = QuadraticEquation (a,b,c)
d=b^2-4*a*c;
if d>=0
disp ('two roots exist')
x1=(-b-sqrt(d))/2*a
x2=(-b+sqrt(d))/2*a
plot(x1,0,'rx',x2,0,'rx')
hold on
x=-10:10
y=a*x.^2+b*x+c
plot(x,y)
hold off
else
disp ('no real roots’)
end
  3 个评论
显示 1更早的评论
Alisha Mistry
Alisha Mistry 2019-12-7
It keeps saying the variables a,b,c aren't defined but i put them into a script as a function so why does it still say that message?
Image Analyst
Image Analyst 2019-12-7
You need to pass in something. You can't just click the green Run triangle on the toolbar. See Matt J's Answer below.

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采纳的回答

Matt J
Matt J 2019-12-7
编辑：Matt J 2019-12-7
[x1,x2] = QuadraticEquation (1,-2,0)
function [x1,x2] = QuadraticEquation (a,b,c)
d=b^2-4*a*c;
if d>=0
disp ('real roots exist')
x1=(-b-sqrt(d))/(2*a); %<---------- brackets in denominator
x2=(-b+sqrt(d))/(2*a); %<---------- brackets in denominator
plot(x1,0,'rx',x2,0,'rx')
hold on
fplot(@(x) a*x.^2+b*x+c) %<---------- fplot is more convenient here
hold off
else
disp ('no real roots') %<---------- missing quote
[x1,x2]=deal([]) %<---------- missing default assignment
end
end
  2 个评论
Grady
Grady 2024-7-12
This code will not work for me I am using 2024a.
Steven Lord
Steven Lord 2024-7-13
What does "will not work" mean in this context?
  • Do you receive warning and/or error messages? If so the full and exact text of those messages (all the text displayed in orange and/or red in the Command Window) may be useful in determining what's going on and how to avoid the warning and/or error.
  • Does it do something different than what you expected? If so, what did it do and what did you expect it to do?
  • Did MATLAB crash? If so please send the crash log file (with a description of what you were running or doing in MATLAB when the crash occured) to Technical Support so we can investigate.
Show us how you tried to use this code as well.

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