how to write a function for quadratic equation?

7 次查看（过去 30 天）
jun
jun 2022-9-24
评论： jun 2022-9-24
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 个评论
Dyuman Joshi
Dyuman Joshi 2022-9-24
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.

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回答（1 个）

Hiro Yoshino
Hiro Yoshino 2022-9-24
Ran in:
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
  1 个评论
jun
jun 2022-9-24
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?

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