unable to overcome syn_sin error message

I am trying to write following script file in matlab for an assignment

function [xx,tt]=syn_sin(fk, Xk,fs,dur,tstart)
if nargin<5
    error('input arguments for the function syn_sin required more')
elseif nargin ==5
        tstart = 0;
end
k=length(fk);
if k~=length(Xk)
    error('Here fk,Xk should be equal elements');
end
[xx,tt]=one_cos(1,0,0,fs,dur,tstart);
for i=1:1:k
    xx=xx+one_cos(fk(i),abs(Xk(i)),angle(Xk(i)),fs,dur,tstart);
end

However I am not able to get this file to do anything but error and I get the following error below

Error using syn_sin

input arguments for the function syn_sin required more

Nothing I try works and I have to use syn_sin so I don't know why there is an error.

Answer 1

[Walter Roberson]

You probably want:

• if nargin<4 give an error message
• if nargin == 4 set tstart = 0

Your current code does not allow 6 or more inputs because there are only 5 input positions and the final one is not varargin

Your current code does not allow 0, 1, 2, 3, or 4 inputs because that is < 5 .

So when you reach the elseif you know that nargin must be 5 exactly. But then you test for 5 (which is certain to be the case if you reach there) and if it is true (which it always will be if you reach the elseif in this code) then you set tstart = 0 -- overwriting any tstart the user might have passed in.