how to write a function for quadratic equation?

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jun 2022-9-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1811635-how-to-write-a-function-for-quadratic-equation

评论： Dyuman Joshi 2022-9-26

I wrote this into matlab but it doesn't work where express x1, x2, it express only one sol in d>=0 but ploting is work in d>=0. and it's error in d<0

why it doen't work and how to fix it?

function [x1,x2] = f(a,b,c)
if a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
end
d=b^2-4*a*c;
if (d>=0)&&(~(a==0))
x1=((-b-sqrt(d))/(2*a));
x2=((-b+sqrt(d))/(2*a));
plot(x1,0,'rx',x2,0,'rx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
elseif a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
else
[x1 x2]=[]
end

4 个评论
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Dyuman Joshi 2022-9-25

Do you want to return empty values for if any/both of the two conditions - a==0 , d<0?

jun 2022-9-25

i want d<0 => empty value return

but a=0&d<0 => x1=x2=-c/b return that i want

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采纳的回答

VBBV 2022-9-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1811635-how-to-write-a-function-for-quadratic-equation#answer_1060265

if (d>=0) & (~(a==0))

use binary operator &

11 个评论
显示 9更早的评论隐藏 9更早的评论

jun 2022-9-26

Are you right about 'a==0'? If 'a=0', an error like this is displayed

Dyuman Joshi 2022-9-26

Let me highlight it. See the green parts, both are same.

I would suggest you to remove the top one and edit last else as

elseif d<0

function [x1,x2] = f(a,b,c)
%{
if a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
end
%}
d=b^2-4*a*c
if (d>=0)&&(~(a==0))
x1=((-b-sqrt(d))/(2*a));
x2=((-b+sqrt(d))/(2*a));
plot(x1,0,'rx',x2,0,'rx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
%{
elseif a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
%}
else
x1 = [];
x2 = [];
end
end