# How to Call a function inside for loop?

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Vaswati Biswas on 19 Nov 2021
Edited: Stephen23 on 19 Nov 2021
I am writing a function like this
function Eqn = eff(neff,hf)
nf=vpa(2.1511);
ns=vpa(1.5264);
nc=vpa(1.3354);
rho=1;
lambda=532.3;
Eqn = (((2*pi./lambda)*(sqrt(nf^2-neff.^2)*hf))-atan((nf/nc)^(2*rho)*sqrt ((neff.^2-nc^2)/(nf^2-neff.^2)))-atan((nf/ns)^(2*rho)*sqrt ((neff^2-ns^2)/(nf^2-neff.^2))) -(m*pi))==0;% equation 8 from paper
end
then I am calling it inside a for loop using the following code
hf = 75:20:350;
m= 0;
NEFF = zeros(size(hf));
for ii=1:numel(hf)
options = optimoptions('fsolve','Display','none','PlotFcn',@optimplotfirstorderopt);
neff = [0,5];
NEFF(ii)=fsolve(@(neff,hf(ii))eff(neff),neff,options
end
plot(hf, NEFF)
But I am getting an error
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for
mismatched delimiters.
what mistake I am making here? Kindly help
Stephen23 on 19 Nov 2021
Your code is missing severay parentheses and that anonymous function is not defined correctly.
Replace this
NEFF(ii)=fsolve(@(neff,hf(ii))eff(neff),neff,options
with something like
fnh = @(n)eff(n,hf(ii));
NEFF(ii) = fsolve(fnh,neff,options);
But I cannot run your code as the objective function needs to be debugged first.

Sulaymon Eshkabilov on 19 Nov 2021
Here is the corrected code, but still you should check the equation. The found roots are complex valued:
hf = 75:20:350;
NEFF = zeros(size(hf));
for ii=1:numel(hf)
options = optimoptions('fsolve','Display','none','PlotFcn',@optimplotfirstorderopt);
neff = [0; 5];
NEFF(ii)=fsolve(@(hf) eff(hf(ii), neff), neff,options);
end
%plot(hf, NEFF)
function F = eff(hf, neff)
nf=(2.1511);
ns=(1.5264);
nc=(1.3354);
rho=(1);
lambda=(532.3);
m=(0);
F = (((2*pi./lambda)*(sqrt(nf^2-neff.^2)*hf))-atan((nf/nc)^(2*rho)*sqrt ((neff.^2-nc^2)/(nf^2-neff.^2)))-atan((nf/ns)^(2*rho)*sqrt ((neff.^2-ns^2)/(nf^2-neff.^2))) -(m*pi));% equation 8 from paper
end
Stephen23 on 19 Nov 2021
"Here is the corrected code.."
Note that this code completely ignores the values of hf defined on the first line. I doubt that is the intent.