function y = cvx_subs2str( x, mask, fieldalt )

if nargin < 2,

mask = [ 1, 1, 1 ];

if nargin < 3,

fieldalt = 0;

if ~isstruct( x ),

error( 'First arugment must be a structure.' );

y = '';

needfield = fieldalt ~= 0;

for k = 1 : length( x ),

try

tp = x(k).type;

catch %#ok

error( 'Invalid subscript structure: field "type" is missing.' );

end

if ~ischar( tp ) || size( tp, 1 ) ~= 1,

error( 'Invalid subscript entry #%d: field "type" must be a string', k );

end

try

sb = x(k).subs;

catch %#ok

error( 'Invalid subscript structure: field "subs" is missing.' );

end

switch tp,

case '.',

if ~ischar( sb ) || size( sb, 1 ) ~= 1,

error( 'Invalid subscript entry #%d: field name must be a string.', k );

elseif ~isvarname( sb ),

error( 'Invalid subscript entry #%d: invalid field name: %s', k, sb );

end

y = [ y, '.', sb ]; %#ok

needfield = 0;

case { '()', '{}' },

if ~mask( 2 )&& tp(1) == '(',

error( 'Invalid subscript entry #%d: array subscripts not allowed here.', k );

elseif ~mask( 3 ) && tp(1) == '{',

error( 'Invalid subscript entry #%d: cell subscripts not allowed here.', k );

elseif needfield,

error( 'Invalid subscript entry #%d: structure field expected here.', k );

elseif ~iscell( sb ),

error( 'Invalid subscript entry #%d: field "subs" must be a cell array.', k );

elseif fieldalt,

needfield = 1;

end

for j = 1 : length( sb ),

if isnumeric( sb{j} ),

sb{j} = sprintf('%g',sb{j});

elseif ~ischar( sb{j} ) || size( sb{j}, 1 ) ~= 1,

error( 'Invalid subscript entry #%d: invalid cell/array subscript', j );

end

end

sb = sprintf( '%s,', sb{:} );

y = [ y, tp(1), sb(1:end-1), tp(2) ]; %#ok

otherwise,

error( 'Invalid subscript entry #%d: invalid subscript tp: %s', k, tp );

end