Unrecognized function or variable for a 'for' loop.

I am trying to compare the penetratino time between two functions. The code was working fine and plotting until I realized that I had made a syntax mistake in the function X10B1T0. I went in and corrected it (swapping the positions of variables), and now the code is not recognizing the "ix". I have deduced that the problem is somewhere in this section of code, but have no idea what it could be.

close all 
clear all
clc 
% %FOR A = 3
% 
x_til = linspace(0,1,10);
dt = 0.1;
tmax = 1;
t_til = linspace(dt,tmax,10);
nt = length(t_til);
nx = length(x_til);
x0 = [0.0000001 1];
tp1 = ones(nt);
tp2 = zeros(nt);
for A = 3 %finding tp actual
    for ix = 1:10
        Tfun1 = @(tp) fX10B1T0(x_til(ix),tp);
        Tfun1A = @(tp) (1*(10^(-A))) - Tfun1(tp);
        tp1(ix) = fzero(Tfun1A,x0);
    end
    for ix = 1:nx
        Tfun2 = @(tp) fX11B10T0(x_til(ix),tp,A);
        Tfun2A = @(tp) (1*(10^(-A))) - Tfun2(tp);
        tp2(ix) = fzero(Tfun2A,x0(1));
    end
end

Error using fzero>localFirstFcnEvalError
FZERO cannot continue because user-supplied function_handle ==> @(tp)(1*(10^(-A)))-Tfun1(tp) failed with the error below.

Unrecognized function or variable 'ix'.

Error in fzero (line 231)
localFirstFcnEvalError(FunFcn,FunFcnIn,ME);

for ix = 1:nx
    for it = 1:nt
        TX10B1T0 = fX10B1T0(x_til,t_til);
    end
    plot (x_til, TX10B1T0(ix,:));
end

Also, here are the functions:

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
for it=1:lengtht % Begin time loop
    xd_ix=xd(ix); % Set current time
    for ix=1:lengthx % Begin space loop
        td_it=td(it); % Set current space
        if td_it == 0 % For time t=0 condition
            T_til1(it,ix)=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
end % function

function [T_til2] = fX11B10T0 (t_til, x_til,A)
lengthx=length(x_til);
lengtht=length(t_til);
T_til2=zeros(lengtht,lengthx); % Preallocating Arrays for speed
for it=1:lengtht % Begin time loop
    td_it=t_til(it); % Set current time
    for ix=1:lengthx % Begin space loop
        xd_ix=x_til(ix); % Set current space
        td_dev1=(1/(10*A))*(2-xd_ix)^2; % First deviation time
        td_dev2=(1/(10*A))*(2+xd_ix)^2; % Second deviation time
        if td_it == 0 % For time t=0 condition
            T_til2(it,ix)=0; % Set inital temperature
        elseif td_it <= td_dev1 % Solution for first small times:
            T_til2(it,ix)=erfc(xd_ix/sqrt(4*td_it));
        elseif td_it > td_dev1 && td_it <= td_dev2 % Solution for second small times:
            T_til2(it,ix)=erfc(xd_ix/sqrt(4*td_it))-erfc((2-xd_ix)/sqrt(4*td_it));
        else
            m_max=ceil(sqrt(A*log(10)/(td_it*pi^2))); % Set max. No. terms
            % Start X11B10T0 case for large times:
            T_til2(it,ix)=1-xd_ix; % steady-state temperature solution
            for m=1:m_max % Continue X11B10T0 case for large times
                % Series solutions:
                betam=m*pi; % Define eigenvalues
                T_til2(it,ix)=T_til2(it,ix)-2*exp(-betam^2*td_it)*sin(betam*xd_ix)/betam;
            end % for m
        end % if td_it
        if xd_ix == 1 % For location x=1 condition
            T_til2(it,ix)=0; % Set x=1 boundary temperature
        end % if xd_ix
    end % for ix
end % for it
end  %function

Answer 1

[Walter Roberson]

for A = 3 %finding tp actual
    for ix = 1:10
        Tfun1 = @(tp) fX10B1T0(x_til(ix),tp);

Tfun1 involves using the current ix value as an index into x_til, but does not involve passing ix to FX10B1T0 -- the element of x_til referenced by ix is passed to that function, but not ix itself.

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
for it=1:lengtht % Begin time loop
    xd_ix=xd(ix); % Set current time

inside the function, the current x_til value is received as x_til, and the tp value is received as t_til . You start executing.. and you get to the line xd_ix=xd(ix) which needs ix which has not been passed in to this function.

Context would suggest that xd_ix = xd(it); instead.

[Matthew Palermo]

That worked! I also ended up making sure the for loop variable was correct so that it reads:

for ix = 1:lengthx

xd_ix = xd(ix);

Thanks