Error using feof, Invalid file identifier. Use fopen to generate a valid file identifier.

fin = fopen('mcs_ansys_standard.txt','rt'); 
    fout = fopen('mcs_ansys.txt','wt');

while ~feof(fin);
  str = fgetl(fin); 
   if strncmp(str,'F,P51X,FY,-',length('F,P51X,FY,-'));
      str =strcat('F,P51X,FY,-',num2str(P)); 
   elseif strncmp(str,'MPDATA,EX,1,,',length('MPDATA,EX,1,,'));
       str =strcat('MPDATA,EX,1,,',num2str(E));
   elseif strncmp(str,'SFBEAM,P51X,1,PRES,',length('SFBEAM,P51X,1,PRES,'));
       str =strcat('SFBEAM,P51X,1,PRES,',num2str(W));
   end
  fprintf(fout, '%s\r\n', str); 

end
fclose(fin); 
fclose(fout);

!"C:\Program Files\ANSYS Inc\v150\ANSYS\bin\winx64\ansys150.exe"  -p ansys -dir "C:\Users\Sirisha\Documents\MATLAB\ranjith" -j "MCS_FEA" -dvt -s read -l en-us -b -i "C:\Users\Sirisha\Documents\MATLAB\ranjith\mcs_ansys.txt" -o "C:\Users\Sirisha\Documents\MATLAB\ranjith\deflecion_out.txt"   

fid = fopen('del_max.out','rt');
flag_string = 'NODE      UY';

while ~feof(fid);
    s = fgets(fid);
    flag = strfind(s,flag_string);
    if flag
        s1 = fgets(fid);
        s2 = fgets(fid);
        s3 = fgets(fid);
        break
    end
end
s = str2num(strtrim(s2));
deflection(i) = -s(2);
fclose('all');

end

Answer 1

[Walter Roberson]

mcs_ansys_standard.txt could not be found on the MATLAB path. It either does not exist at all, or is in some directory that is not on the MATLAB path.