On run 'example/sumo/grid.py'.FatalFlowError:'Not enough vehicles have spawned! Bad start?' - sumo

Question

I want to simulate a jam simulation on the grid example,
So I try to increase the number of row and column or increase the number of num_cars_left/nums_cars_right/nums_cars_top/nums_cars_bot.
For example:
n_rows = 5
n_columns = 5
num_cars_left = 50
num_cars_right = 50
num_cars_top = 50
num_cars_bot = 50
So, then run it by command, there is an error:
Loading configuration... done.
Success.
Loading configuration... done.
Traceback (most recent call last):
File "examples/sumo/grid.py", line 237, in <module>
exp.run(1, 1500)
File "/home/dnl/flow/flow/core/experiment.py", line 118, in run
state = self.env.reset()
File "/home/dnl/flow/flow/envs/loop/loop_accel.py", line 167, in reset
obs = super().reset()
File "/home/dnl/flow/flow/envs/base_env.py", line 520, in reset
raise FatalFlowError(msg=msg)
flow.utils.exceptions.FatalFlowError:
Not enough vehicles have spawned! Bad start?
Missing vehicles / initial state:
- human_994: ('human', 'bot4_0', 0, 446, 0)
- human_546: ('human', 'top0_5', 0, 466, 0)
- human_886: ('human', 'bot3_0', 0, 366, 0)
- human_689: ('human', 'bot1_0', 0, 396, 0)
.....
And then I checked the 'flow/flow/envs/base_env.py'
There is a description of it:
# check to make sure all vehicles have been spawned
if len(self.initial_ids) > len(initial_ids):
missing_vehicles = list(set(self.initial_ids) - set(initial_ids))
msg = '\nNot enough vehicles have spawned! Bad start?\n' \
'Missing vehicles / initial state:\n'
for veh_id in missing_vehicles:
msg += '- {}: {}\n'.format(veh_id, self.initial_state[veh_id])
raise FatalFlowError(msg=msg)
So, my question is: if there is a limit number of rows, columns, nums_cars_left(right/bot/top) if I want to simulate a traffic jam on grid, how to do?

Answer 1

The grid example examples/sumo/grid.py doesn't use inflows by default,
instead it spawns the vehicles directly on the input edges. So if you increase the number of vehicles, you have to increase the size of the edges they spawn on. I tried your example and this setting works for me:
inner_length = 300
long_length = 500
short_length = 500
n_rows = 5
n_columns = 5
num_cars_left = 50
num_cars_right = 50
num_cars_top = 50
num_cars_bot = 50
The length of the edges the vehicles spawn on is short_length, it is the one you want to increase if the vehicles don't have enough room to be added.
Also, changing the number of rows and columns doesn't change anything because 50 vehicles will be added to each of them; so in this case you will have 20 input edges of each 50 vehicles, 1000 vehicles total, which will be quite laggy.
If you want to use continuous inflows instead of one-time spawning, have a look at the use_inflows parameter in the grid_example function in examples/sumo/grid.py, and what this parameter does when it's set to True.