Using block names like 'Transfer Fcn' works only if you use the full block path as follows:
add_block('simulink/Continuous/Transfer Fcn', 'untitled/Transfer Fcn')
Otherwise, you can use 'built-in/blocktype' as a source block path name for Simulink built-in blocks, where blocktype is the built-in block type (that is, the value of its BlockType parameter (see Common Block Properties). However, using 'built-in/blocktype' causes some default parameter values of some blocks to be different from the defaults that you get if you added those blocks interactively using Simulink.
add_block('built-in/TransferFcn', 'untitled/Transfer Fcn1')
