function res=wrifi(m,n,N,i)
    X=zeros(m,n); // on simule m trajectoires de longueur n
    indice=[];
    temp0=[];
    tempN=[];
    for k=1:m
        z=i*ones(1,n);
        for j=1:(n-1);
            z(1,j+1)=grand(1,1,"bin",N,z(1,j)/N);            
        end
        X(k,:)=z;
        // on ne retient que les marches qui touchent zero ou N  
        test1=bool2s((X(k,$)==0));
        test2=bool2s((X(k,$)==N));
        if (test1==1) then
            indice=[indice ; k];
            temp0=[temp0 ; sum(bool2s((z>0)))+1];
        elseif (test2==1) then
            indice=[indice ; k];
            tempN=[tempN ; sum(bool2s(((N-z)>0)))+1];
        end
    end
    Z=X(indice,:);
    dernier=Z(:,$)/N;
    x=i/N;
    a=-2*N*(x*log(x)+(1-x)*log(1-x));
    b=mean(temp0);
    c=mean(tempN);
    d=mean([temp0 ; tempN]);
    res=[mean(dernier) a b c d];
endfunction