Error when running this code.

Can anyone explain why I'm getting this error when I run this code.

   assignment3_2
  Undefined function or variable 'lorenz_attractor'.

Error in odearguments (line 87)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.

Error in ode45 (line 115)
    odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in assignment3_2 (line 2)
[t1, y1] = ode45(@lorenz_attractor,tspan,y0);

Here's the code

function [a, r2] = assignment3(XX,YY)
% linregr: linear regression curve fitting
%   [a, r2] = linregr(x,y): Least squares fit of straight
%           line to data by solving the normal equations
% input:
%   x = independent variable
%   y = dependent variable
% output:
%   a = vector of slope, a(1), and intercept, a(2)
%   r2 = coefficient of determination
n = length(XX);
if length(YY)~=n, error('x and y must be same length'); end
XX = XX(:); YY = YY(:); % convert to column vectors
sx = sum(XX); sy = sum(YY);
sx2 = sum(XX.*XX); sxy = sum(XX.*YY); sy2 = sum(YY.*YY);
a(1) = (n*sxy-sx*sy)/(n*sx2-sx^2);
a(2) = sy/n-a(1)*sx/n;
r2 = ((n*sxy-sx*sy)/sqrt(n*sx2-sx^2)/sqrt(n*sy2-sy^2))^2;
% create plot of data and best fit line
xp = linspace(min(XX),max(XX),2);
yp = a(1)*xp+a(2);
plot(XX,YY,xp,yp)
grid on

And this is the script I am running.

tspan = [0 30]; y0 = [5 5 5]; y00 = [5.00001 5 5];
[t1, y1] = ode45(@lorenz_attractor,tspan,y0);
[t2, y2] = ode45(@lorenz_attractor,tspan,y00);

y21 = interp1(t2,y2,t1);

Y = log(abs(y21(:,3)- y1(:,3)));
X = t1;
XX = X(266:891,1);
YY = Y(266:891,1);
lin = assignment3(XX,YY)

[Star Strider]

You have not defined a function named ‘lorenz_attractor’.

You would have to define it for example as:

function [t,y] = lorenz_attractor(t,y)
    ... CODE ...
end

[Westin Messer]

When I put that in my script file I still got the same error.

[dpb]

Can't define functions in script files.

There has to be a pre-existing function of the name in an m-file on the searchable MATLABPATH that will show up when run the script.

There is a packaged demo lorenz with Matlab distribution but no builtin lorenz_attractor. I presume given the comment at the top of the code this came from some coursework code somewhere; you've not downloaded the complete code (or were to supply the function yourself, maybe???).