现代数值数学和计算习题答案(同济版)(6)

:

b2 4ac

1

c=0

b

(Vieta)

)

a=0

b=0

(

function[x,flag]=root2qe(a,b,c)

ifnargin==1,

c=a(3);b=a(2);a=a(1);end

ifa~=0,%Solve2-orderequation

M=max(abs([a,b,c]));%scalinga=a/M;b=b/M;c=c/M;s=sign(b);

ifs==0,s=1;end

x1=(-b-s*sqrt(b^2-4*a*c))/2/a;x2=c/(a*x1);%avoidlargeerrorx=[x1x2]’;

flag=’twosolutions’;elseifb~=0,%Solve1-orderequation

x=-c/b;

flag=’onesolution’;elseifc~=0,%nonzeroconstant

x=[];

flag=’noxisasolution’;else%equality0=0

x=[1];

flag=’allxaresolutions’;end

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