how to use fzero is for loop?

Question

Dameon Solestro 2021-12-11

回答： Dyuman Joshi 2021-12-11

Im trying to solve quadratic formulas in for-loop where the previous x value is needed for the next loop.

x(1)=10
for i=2:4
    f=@(x) (x(i)^2)-(3*x(i)*(x(i-1)))-4
    x(i)=fzero(f,0,[])
end
x'

Error using fzero>localFirstFcnEval (line 729)

FZERO cannot continue because user-supplied

function_handle ==> @(x)(x(i)^2)-(3*x(i)*(x(i-1)))-4

failed with the error below.

Index exceeds the number of array elements. Index

must not exceed 1.

Error in fzero (line 286)

fx = localFirstFcnEval(FunFcn,FunFcnIn,x,varargin{:});

Error in randnot (line 3)

x(i)=fzero(f,0,[])

Is there any way to fix this??

Answer 1

Dyuman Joshi 2021-12-11

How exactly will your f be defined if x(i) is not defined. Not sure what you want to do but, Try this -

x(1)=10;
for i=2:4
    y=roots([1 -3*x(i-1) -4]);
    x(i) = y(abs(y)==min(abs(y)));
end
x'
ans = 4×1
   10.0000
   -0.1327
    1.8108
   -0.6569