name=input('Enter name of input text file : ','s');
%name='in_2';
name=strcat(name,'.txt');
fileid=fopen(name, 'r');
formatspec= '%f';
sizea=inf;
A = fscanf(fileid,formatspec,sizea);
fclose(fileid);
n=A(1);
mat=(reshape(A(2:n*n+1),n,n))';
tol=A(n*n+2);
choose=input('what do you need? (l/a) \nl-largest eigenvalue \na-all eigenvalues \n','s');
if choose=='l'
    [l,v,i]=powme(mat,n,tol)
    fileid=fopen('out_2l.txt','w');
    fprintf(fileid,'Largest eigenvalue \n');
    fprintf(fileid,'%f\n',l);
    fprintf(fileid,'Eigenvectors \n');
    fprintf(fileid,'%f\n',v);
    fprintf(fileid,'No. of iterations\n%d\n',i);
    fprintf(fileid,'\n');
    fclose(fileid);
end

if choose=='a'
    [ev,i]=qrev(mat,n,tol)
    fileid=fopen('out_2a.txt','w');
    fprintf(fileid,'Eigenvalues \n');
    fprintf(fileid,'%f\n',ev);
    fprintf(fileid,'No. of iterations\n%d\n',i);
    fclose(fileid);
end

function [l,v,i]=powme(mat,n,tol)
z=zeros(n,1);
z(1)=1;
y=z;
i=0;
while 1
    i=i+1;
    y=z/norm(z,2);
    z=mat*y;
    yo=y;
    y=z/norm(z,2);
    z=mat*y;
    if norm(y-yo,Inf)*100<=tol
        break
    end
end
l=(y')*z;
v=y;
end

function [ev,ic]=qrev(mat,n,tol)
ic=0;
while 1
    ic=ic+1;
    q=zeros(n,n);
    z=zeros(n,1);
    q(:,1)=mat(:,1)/norm(mat(:,1),2);
    for k=1:n-1
        sum=zeros(n,1);
        for i=1:k
            sum=sum+((mat(:,k+1)')*q(:,i))*q(:,i);
        end
        z=mat(:,k+1)-sum;
        q(:,k+1)=z/norm(z,2);
    end
    r=q'*mat;
    lo=diag(mat);
    mat=r*q;
    l=diag(mat);
    if norm(l-lo,Inf)*100<=tol
        break;
    end
end
ev=l;
end