%% Returns column of indices in the slowness vector corresponding to selected
%% rows and columns in the spatial grid
%% ======================================================================================
%%
%% Parameters:
%%	model - structure describing the 2D rectangular model.
%%	rows - one or multiple numbers of rows (depth levels) in the grid  
%%	cols - one or multiple numbers of columns (horizontal distances) in the grid

%% Returns:
%%	ind - indices of rows in the slowness model vector corresponding to (rows,cols)

function ind = grid_block(model,rows,cols)

  ind = [];

  nr = length(rows);
  nc = length(cols);

  rcol = reshape(cols,nc,1);		% list of column numbers as a column

  for i=1:nr
  	ind = [ ind; ones(nr,1)*(rows(i)-1)*model.nx + rcol ];
  end

end