def set_types(self, syn_type, nodes=None, fraction=None):
'''
Set the synaptic/connection types.
.. warning ::
The special "type" attribute cannot be modified when using graphs
that inherit from the :class:`~nngt.Network` class. This is because
for biological networks, neurons make only one kind of synapse,
which is determined by the :class:`nngt.core.NeuralGroup` they
belong to.
Parameters
----------
syn_type : int or string
Type of the connection among 'excitatory' (also `1`) or
'inhibitory' (also `-1`).
nodes : int, float or list, optional (default: `None`)
If `nodes` is an int, number of nodes of the required type that
will be created in the graph (all connections from inhibitory nodes
are inhibitory); if it is a float, ratio of `syn_type` nodes in the
graph; if it is a list, ids of the `syn_type` nodes.
fraction : float, optional (default: `None`)
Fraction of the selected edges that will be set as `syn_type` (if
`nodes` is not `None`, it is the fraction of the specified nodes'
edges, otherwise it is the fraction of all edges in the graph).
Returns
-------
t_list : :class:`numpy.ndarray`
List of the types in an order that matches the `edges` attribute of
the graph.
'''
inhib_nodes = nodes
if syn_type == 'excitatory' or syn_type == 1:
if issubclass(nodes.__class__, int):
inhib_nodes = graph.node_nb() - nodes
elif issubclass(nodes.__class__, float):
inhib_nodes = 1./nodes
elif hasattr(nodes, '__iter__'):
inhib_nodes = list(range(graph.node_nb()))
nodes.sort()
for node in nodes[::-1]:
del inhib_nodes[node]
return Connections.types(self, inhib_nodes, fraction)
