function openfemm(fn)

    global ifile ofile IsMatlab HandleToFEMM

    rootdir=tilde_expand('~/.wine/drive_c/femm42/bin/');
    IsMatlab=0;

    % define temporary file locations
    ifile=[rootdir,'ifile.txt'];
    ofile=[rootdir,'ofile.txt'];

    % test to see if there is already a femm process open
    try
        [fid,msg]=fopen(ifile,'wt');
    catch
        [fid,msg]=fopen(ifile,'w');
    end
    fprintf(fid,'flput(0)');
    fclose(fid);
    sleep(0.25);
    try
        [fid,msg]=fopen(ofile,'rt');
    catch
        [fid,msg]=fopen(ofile,'r');
    end
    if (fid==-1)
        unlink(ifile);
        system(['wine "',rootdir,'femm.exe" -filelink 2> /dev/null'],1,'async');
    else
        fclose(fid);
        unlink(ofile);
        disp('FEMM is already open');
    end