How to avoid dividing by zero in this function?

I fixed a previous issue of constant values and now the challenge is figuring out how to avoid dividing by zero. I figured that simply advacing the time steps would help, but it did not. Any help is much appreciated.

%```
function [T_til1] = fX10B1T0 (x_til, t_til)
lengthx=length(x_til);
lengtht=length(t_til);
T_til1=zeros(lengthx,lengtht); % Preallocating Arrays for speed
% xd = ones(lengthx);
% td = ones(lengtht);
for ix=1:lengthx % Begin time loop
    xd_ix=x_til(ix); % Set current time
    for it=1:lengtht % Begin space loop
        td_it=t_til(it); % Set current space
        if td_it == 0 % For time t=0 condition
            T_til1(it+1,ix+1)=0; % Set inital temperature
        else
            % Solution at any time
            T_til1(ix,it)=erfc(xd_ix/sqrt(4*td_it));
        end % if td_it
    end % for ix
end % for it```

[Mathieu NOE]

I don't see any issue in the posted code

if td_it is >0 there should be no division by zero in T_til1(ix,it)=erfc(xd_ix/sqrt(4*td_it))

[Walter Roberson]

You should probably be storing into the same location in both branches.