You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: boost_ada.m
    path of file: ./repos/malini/Classifiers/Boosted Stumps/Classifier_Files/AdaBoost Matlab
    
    the code of the file until where you have to start completion: 
% combine at most 'ncomp' stumps

function [model] = boost_ada(X,y,ncomp)

W = ones(size(X,1),1); 
W = W/sum(W);
alpha = 1;

model = cell(
    
function [model] = boost_ada(X,y,ncomp)

W = ones(size(X,1),1); 
W = W/sum(W);
alpha = 1;

model = cell(ncomp,1);

H = zeros(size(X,1),1);
for i=1:ncomp,
  stump = build_stump(X,y,W);
   
  if ( stump.werr < 0.5&& stump.werr > 0.000001),
    h = eval_stump(stump,X);
    
    % insert alpha calculation here
    alpha = 0.5*log((1-stump.werr)/stump.werr);
    
    H = H + alpha*h; % update the combined predictions
    
    % weight update
    W=exp(-H.*y);
    W=W/sum(W);
    
    model{i} = stump;
    model{i}.alpha = alpha; 
  else  
      if i > 1
        i = i-1; break; 
      else
          model{i} = stump;
          model{i}.alpha = 1;
          break;
      end