how to write a function for quadratic equation?

5 views (last 30 days)
jun
jun on 24 Sep 2022
Commented: jun on 24 Sep 2022
I wrote this into matlab but it doesn't work where a=0, can someone explain why?
how can find x1, x2 where a=0?
function [x1,x2] = f (a,b,c)
d=b^2-4*a*c;
if d>=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
else
[x1,x2]=deal([])
end
end
  1 Comment
Dyuman Joshi
Dyuman Joshi on 24 Sep 2022
If a=0, then it's a straight line, it will only intersect the x-axis once.
Also, if a=0 then the expressions
x1=(-b-sqrt(d))/(2*a);
x2=(-b+sqrt(d))/(2*a);
will become not defined.
You have to write a special condition for a=0, according to what you expect.

Sign in to comment.

Answers (1)

Hiro Yoshino
Hiro Yoshino on 24 Sep 2022
You can check the arguments before evaluating your statements this way:
[x1,x2] = f(1,-2,1)
x1 = 1
x2 = 1
[x1,x2] = f(0,-2,1)
Error using solution>f
Invalid argument at position 1. Value must not be zero.
function [x1,x2] = f(a,b,c)
arguments
a (1,1) {mustBeNonzero}
b (1,1) {mustBeReal}
c (1,1) {mustBeReal}
end
d=b^2-4*a*c;
if d>=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
else
[x1,x2]=deal([])
end
end
  1 Comment
jun
jun on 24 Sep 2022
it semms only a=non-zero case by argument state, did i understnad correctey?
If a=0 and non-a=/=0 situations need to be written separately as without setting arguments,
Where and how to add conditions for a=0 and a=/=0 situations?

Sign in to comment.

Categories

Find more on Tables in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!