Power_Method_forEigenValueNVectors.m

clear;clc
% Power Method Algorithm 
 A=input('Input matrix: ')
 x=input('Input Initial approximation as row vector: ');
 
 n=length(x);
 
 y = zeros(1,n);
 tol = input('Enter the tolerance, tol: ');
 m = input('Enter maximum number of iterations, m:  ');
 

 
 
 k = 1; lp = 1;
 amax = abs(x(1));
 for i = 2 : n 
    if abs(x(i)) > amax 
        amax = abs(x(i));
        lp = i;
    end
 end  
 
 
 fprintf('\n\n  Ite.    Eigenvalue     ............Eigenvectores............\n');
 while k <= m  
      for i = 1 : n 
         y(i) = 0;
         for j = 1 : n 
           y(i) = y(i) + A(i,j) * x(j);
         end
      end
      ymu = max(y);
      lp = 1;
      amax = abs(y(1));
      for i = 2 : n 
         if abs(y(i)) > amax 
            amax = abs(y(i));
            lp = i;
         end
      end
      if amax <= 0 
         fprintf('0 eigenvalue - select another ');
         fprintf('initial vector and begin again\n');
      else
           err = 0;
           for i = 1 : n 
              t = y(i)/y(lp);
              if abs(x(i)-t) > err 
                err = abs(x(i)-t);
              end
              x(i) = t;
           end
           fprintf('%4d     %11.8f', k, ymu);
           for i = 1 : n 
             fprintf('   %11.8f', x(i));
           end
           fprintf('\n');
           if err <= tol 
              fprintf('\n\nThe eigenvalue after %d iterations is: %11.8f \n',k, ymu);
              fprintf('The corresponding eigenvector is: \n');
              for i = 1 : n 
                 fprintf('                                 %11.8f \n', x(i));
              end
              fprintf('\n');
              break;
           end
           k = k+1;
       end
 end 
 if k > m 
 fprintf('Method did not converge within %d iterations\n', m);
 end