Why do I get the error "Undefined function 'function name' for input arguments of type 'cell'"

For a university assignment I need to compute the fixed modes of a system using a function given to us students by the professor.

The matrices are defined as such:

Atot = [0 -1 -2/3 0 0 0 0
        1 0 -2/3 0 0 0 0
        -3 0 -3 0 0 0 0
        0 1 0 -1 0 0 0
        0 0 0 0 -3/2 0 -1/4
        0 3/2 0 0 -1 -1 0
        0 0 0 0 1 0 -1/2];
    
Bdec{1}=[0 2 4 0 0 2 0]';
Bdec{2}=[0 0 0 -1 0 0 0]';
Bdec{3}=[0 0 0 0 1 -2 0;
        0 0 0 0 0 -1 0]';

Ctot=eye(7);

Cdec{1}=Ctot(1:3,:);
Cdec{2}=Ctot(4,:);
Cdec{3}=Ctot(5:7,:);

And the function takes as input:

function [Difm]=di_fixed_modes(Atot,Baggr,Caggr,N,ContStruc,rounding_n)
% Computes the fixed modes of the system, with reference to the control
% information structure specified by 'ContStruc'.
%
% Inputs:
% - Atot: system matrix - either continuous-time or discrete-time.
% - Baggr: input matrices - either continuous-time or discrete-time -
% (i.e., Baggr{1},..., Baggr{N} are the input matrices of the decomposed system, one for each channel).
% - Caggr: output matrices - either continuous-time or discrete-time -
% (i.e., Caggr{1},..., Caggr{N} are the output matrices of the decomposed
% system, one for each channel).
% - N: number of subsystems.
% - ContStruc: NxN matrix that specifies the information structure
% constraints (ContStruc(i,j)=1 if communication is allowed between channel
% j to channel i, ContStruc(i,j)=0 otherwise).
% - rounding_n: the eigenvalues are rounded at the nth decimal place 
%
% Output:
% - Difm: vector containing the fixed modes (if empty, there are no FMs)

But when I call the function this error "Undefined function 'di_fixed_modes' for input arguments of type 'cell'" appears, even though the function is designed for the cell type of input for the matrices B and C. This is the only part where they're used:

Btot=[];
Ctot=[];
for i=1:N
    m(i)=size(Baggr{i},2);
    p(i)=size(Caggr{i},1);
    Btot=[Btot,Baggr{i}];
    Ctot=[Ctot
        Caggr{i}];
end

[Voss]

Could it be that di_fixed_modes.m is not on the MATLAB path? Type this on the command line and see what comes back:

which di_fixed_modes -all

[Giosuè Basso]

Thank you so much, of course it was this easy.

Now the problem is understanding why no fixed modes are returned but I guess I'll need to figure it out by myslef.

Thanks again