Problems whit syms: Variable "iv" has been previously used as a function or command name

Hi! While running this code

function [nfx,nfxp,nfy,nfyp] = rw
%This program computes a log-linear approximation to the  function f for a small open economy without stationarity inducing features. The model is described in ``Closing Small Open Economy Models,'' by Stephanie Schmitt-Grohe and Martin Uribe. The function f defines  the DSGE model (a p denotes next-period variables) : 
%  E_t f(yp,y,xp,x) =0. 
%
%Inputs: none
%
%Output: Numerical first derivative of f
%
%Calls: anal_deriv.m num_eval.m rw_ss.m
%
%(c) Stephanie Schmitt-Grohe and Martin Uribe
%
%Date November 8, 2001

%Define parameters

approx = 1; %Order of approximation desired

syms GAMA DELTA ALFA RHO OMEGA PHI R DBAR 

%Define variables 
syms c cp k kp k1 k1p a ap h hp d dp  yy yyp iv ivp tb tbp la lap tby tbyp cay cayp    

%Give functional form for utility and production functions
u = ((c - h^OMEGA/OMEGA)^(1-GAMA)-1)/(1-GAMA);
up = ((cp - hp^OMEGA/OMEGA)^(1-GAMA)-1)/(1-GAMA);
output = a * k^ALFA *  h^(1-ALFA);
outputp = ap * kp^ALFA *  hp^(1-ALFA);

%Write equations (e1, e2,...en)
%Note: we take a linear, rather than log-linear, approximation with respect to tb, the trade balance)
e1 = (1+R) * d - log(tb) - dp;

e2 = -log(tb) + yy - c - iv - PHI/2 * (kp -k)^2;

e3 = -yy + a * k^ALFA *  h^(1-ALFA);

e4 = -iv + kp - (1-DELTA) *k;

e5 = - la + lap;

e6 = - la + diff(u,'c');

e7 = -diff(u,'h') - la * diff(output,'h');

e8 = -la * (1+ PHI*(kp-k)) + 1 / (1+R) *  lap* (diff(outputp,'kp') + 1 - DELTA + PHI * (k1p -k1));

e9 = -k1 + kp;

e10 = -log(ap) + RHO * log(a); 

e11 = -log(tby) + log(tb) / yy; 

e12 = -log(cay) - R*d / yy + log(tby); 

%Create function f

f = [e1;e2;e3;e4;e5;e6;e7;e8;e9;e10;e11;e12];

% Define the vector of controls, y, and states, x

x = [k d a];

y = [yy c iv h tby cay tb la k1];

xp = [kp dp ap];

yp = [yyp cp ivp hp tbyp cayp tbp lap k1p];

%Make f a function of the logarithm of the state and control vector
f = subs(f, [x,y,xp,yp], exp([x,y,xp,yp]));

%Compute analytical derivatives of f
[fx,fxp,fy,fyp]=anal_deriv(f,x,y,xp,yp,approx);

%Numerical evaluation

%Assign values to parameters and steady-state variables
[GAMA,DELTA,ALFA,RHO,OMEGA,PHI,R,DBAR,c,cp,h,hp,k,kp,k1,k1p,d,dp,iv,ivp,tb,tbp,la,lap,yy,yyp,a,ap,tby,tbyp,cay,cayp]=rw_ss;

%Compute numerical derivatives of f
num_eval

Matlab give me this error message:

   Error: File: rw_or.m Line: 81 Column: 66
  Variable "iv" has been previously used as a function or command name

I also attached here the code of anal_deriv

function [fx,fxp,fy,fyp,fypyp,fypy,fypxp,fypx,fyyp,fyy,fyxp,fyx,fxpyp,fxpy,fxpxp,fxpx,fxyp,fxy,fxxp,fxx]=anal_deriv(f,x,y,xp,yp,approx); 
%[fx,fxp,fy,fyp,fypyp,fypy,fypxp,fypx,fyyp,fyy,fyxp,fyx,fxpyp,fxpy,fxpxp,fxpx,fxyp,fxy,fxxp,fxx]=anal_deriv(f,x,y,xp,yp,approx); 
% Computes analytical first and second (if approx=2) derivatives of the function f(yp,y,xp,x) with respect to x, y, xp, and yp.  For documentation, see the paper ``Solving Dynamic General Equilibrium Models Using a Second-Order Approximation to the Policy Function,'' by Stephanie Schmitt-Grohe and Martin Uribe, 2001). 
%
%Inputs: f, x, y, xp, yp, approx
%
%Output: Analytical first and second derivatives of f. 
%
%If approx is set at a value different from 2, the program delivers the first derivatives of f and sets second derivatives at zero. If approx equals 2, the program returns first and second derivatives of f. The default value of approx is 2. 
%Note: This program requires MATLAB's Symbolic Math Toolbox
%
%(c) Stephanie Schmitt-Grohe and Martin Uribe
%Date July 17, 2001

if nargin==5
approx=2;
end

nx = size(x,2);
ny = size(y,2);
nxp = size(xp,2);
nyp = size(yp,2);

n = size(f,1);

%Compute the first and second derivatives of f
fx = jacobian(f,x);
fxp = jacobian(f,xp);
fy = jacobian(f,y);
fyp = jacobian(f,yp);

if approx==2

fypyp = reshape(jacobian(fyp(:),yp),n,nyp,nyp);

fypy = reshape(jacobian(fyp(:),y),n,nyp,ny);

fypxp = reshape(jacobian(fyp(:),xp),n,nyp,nxp);

fypx = reshape(jacobian(fyp(:),x),n,nyp,nx);

fyyp = reshape(jacobian(fy(:),yp),n,ny,nyp);

fyy = reshape(jacobian(fy(:),y),n,ny,ny);

fyxp = reshape(jacobian(fy(:),xp),n,ny,nxp);

fyx = reshape(jacobian(fy(:),x),n,ny,nx);

fxpyp = reshape(jacobian(fxp(:),yp),n,nxp,nyp);

fxpy = reshape(jacobian(fxp(:),y),n,nxp,ny);

fxpxp = reshape(jacobian(fxp(:),xp),n,nxp,nxp);

fxpx = reshape(jacobian(fxp(:),x),n,nxp,nx);

fxyp = reshape(jacobian(fx(:),yp),n,nx,nyp);

fxy = reshape(jacobian(fx(:),y),n,nx,ny);

fxxp = reshape(jacobian(fx(:),xp),n,nx,nxp);

fxx = reshape(jacobian(fx(:),x),n,nx,nx);

else

fypyp=0; fypy=0; fypxp=0; fypx=0; fyyp=0; fyy=0; fyxp=0; fyx=0; fxpyp=0; fxpy=0; fxpxp=0; fxpx=0; fxyp=0; fxy=0; fxxp=0; fxx=0;

end

I'd appreciate some help! Thanks!

[Walter Roberson]

Difficult to say without the complete source. The file name from the error message does not match any function you show here, and the line number matches a comment.