params2stack.m

function stack = params2stack(params, ei)

% Converts a flattened parameter vector into a nice "stack" structure 
% This is useful when you're building multilayer networks.
%
% stack = params2stack(params, netconfig)
%
% params - flattened parameter vector
% ei - auxiliary variable containing 
%             the configuration of the network


% Maps the params (a vector into a stack of weights)
depth = numel(ei.layer_sizes);
stack = cell(depth,1);
% the size of the previous layer
prev_size = ei.input_dim; 
% marks current position in parameter vector
cur_pos = 1;

for d = 1:depth
    % Creates layer d
    stack{d} = struct;

    hidden = ei.layer_sizes(d);
    % Extracts weights
    wlen = double(hidden * prev_size);
    stack{d}.W = reshape(params(cur_pos:cur_pos+wlen-1), hidden, prev_size);
    cur_pos = cur_pos+wlen;

    % Extracts bias
    blen = hidden;
    stack{d}.b = reshape(params(cur_pos:cur_pos+blen-1), hidden, 1);
    cur_pos = cur_pos+blen;
    
    % Sets previous layer size
    prev_size = hidden;
    
end

end