How can i solve the error Undefined function 'cxroot' for input arguments of type 'char'.?

i =1;

for a = 1.5 : 0.001 : 1.6

lambda11=a.*10^-6;

C=3e8 ;

Epsilond =3.61 ;

W=2*pi*C./lambda11;

K0=2*pi./lambda11;

WP=1.3605e16 ;

gamma=(1.7352e13 );

A=W.^2+1i*gamma*W

Epsilonm=1-((WP*WP)/A);

h=((Epsilonm*Epsilond)/(Epsilonm+Epsilond));

beta=K0*sqrt(h);

neff=beta/K0 ;

lambda1(i)=lambda11 ;

neff1(i)=real(neff);

i =i+1;

end

global lambda ;

Nmax=50;

tol =5.1*10^6 ;

h=1.88;

i =1;

for a=1.5:0.01:1.6

lambda=a.*10^-6;

x1=cxroot('project',h);

y=x1;

y1(i)=real(x1);

y2(i)=imag(x1);

lambda12(i)=lambda;

i=i+1;

end

plot(lambda1,neff1,lambda12, y1)

Answer 1

[Walter Roberson]

https://www.mathworks.com/matlabcentral/fileexchange/22661-cxroot-complex-root-of-complex-function