how to write a function for quadratic equation?

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

[Dyuman Joshi]

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.

Answer 1

[Hiro Yoshino]

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

For further detail, go and visit https://www.mathworks.com/help/matlab/matlab_prog/function-argument-validation-1.html

[jun]

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?