Unrecognized function or variable 'msr_error'.

Unrecognized function or variable 'msr_error'.

Error in final (line 25)

Err_b1=msr_error(o,out,256,256);

[Mathieu NOE]

it simply tells you that no variable or function (in the known paths) that exist with this name

there is such a function that exist in this FEX, if it's what you miss :

Back projections and tensor transform - File Exchange - MATLAB Central (mathworks.com)

%   Call: msr_error.m
%	To calculate error of two images
%
%	Artyom Grigoryan, EE TAMU 1997
function Err=msr_error(o,out,N1,N2)
   Err=0.;   
   N=sqrt(N1*N2);
	for j=1:N1 
      for k=1:N2
         t=out(j,k)-o(j,k); 
         t=t/N; 
         Err=Err+t*t;	
      end
    end
   Err=sqrt(Err)/N;