B$.$ Study the function code given and answer the questions that follow.

function $[$root$,fx,ea,$iter $]$ bisect $($func$,x1,xu,$ es$,$ maxit, varargin$)$

If nargin error$(\text{'}$at least $3$ input arguments required'$),$ end

test $=$func$(x1,$varargin$\{\begin{array}{c}?\end{array})***func(xu,$varargin$\{\begin{array}{c}?\end{array})$;

if test$>0,$ error $(\text{'}$no sign change'$),$ end

If nargin$<mn\; id="EditorElement\_723744">4</mn><mi\; id="EditorElement\_723745">|</mi><mi\; id="EditorElement\_723746">|</mi>$isempty$($es$),$ es$=0\mathrm{.}0001$; end

if nargin$<mn\; id="EditorElement\_723785">5</mn><mi\; id="EditorElement\_723786">|</mi><mi\; id="EditorElement\_723787">|</mi>$isempty$($maxit$),$ maxit$=50$; end

iter $=0$;$r=1$; ea $=100$;

while $(1)$

xrold$=xr$;

$xr=\frac{xl+xu}{2}$;

iter $=$ iter $+1$ ;

if $xr=0,$ ea $\frac{?}{a}=bs(\frac{xr-\text{x}\text{r}\text{o}\text{l}\text{d}}{x}r)***100$; end

test $=$func$(xl,$varargin$\{\begin{array}{c}?\end{array})***func(xr,$varargin$\{\begin{array}{c}?\end{array})$;

if test $<mn\; id="EditorElement\_723204">0</mn>$

$xu=xr$;

elseif test $>0$

$xl=xr$;

else

$ea=0$;

end

if ea es $||$ iter $>=$ maxit, break, end

end

$\sqrt[\phantom{2}]{x}=r$;$fx=$func$(xr,$varargin$\{\begin{array}{c}?\end{array})$;

What does this function?

Look up the MATLAB function varargin employed in the function script above. What is varargin and what is it used for?

What are the default values for es and maxit in the function call below?

$>$val$=$bisect$($ func $,xl,xu)$

If line $14$ is true, which interval is represented by line $15?$