fix a bug in iterative solving for DC LDO.
clean some comments.
delete an undefined function in circuit.cpp.
working on optimize LDO locations with fixed numbers.
working on moving LDOs in ckt_l.
working on building graph function.
extracting control nodes for the pads.
add more functions.
adding old functions for moving ldos.
add move violation pads.
add graph_move_pads().
add clear_flags().
working on LDO ideal node not within block.
add mark_geo_flag() in subcircuit.cpp.
add function judging whether node is in blocks.
still working on relocate LDOs.
delete some unused functions.
finish project ldo node().
rebuilding the nets from LDO movement.
working on rebuilding_global_nets().