# A Cosimulation Example
This is an example of a simple sender and receiver Python HELICS federation.
# Simple cosimulation between sender and receiver
Send any floating point value from simulation time 5 to simulation time 10 from one process to another.
If you'd like to try to build this yourself, you can.
# Implementation
We need two processes. We need the a sender.py:
# -*- coding: utf-8 -*-
import os
import helics as h
from math import pi
fed = h.helicsCreateCombinationFederateFromConfig(
os.path.join(os.path.dirname(__file__), "sender.json")
)
topicA = h.helicsFederateGetPublication(fed, "topicA")
h.helicsFederateEnterExecutingMode(fed)
currenttime = 0
for t in range(5, 10 + 1):
while currenttime < t:
currenttime = h.helicsFederateRequestTime(fed, t)
print(f"Sending value = {pi} at time = {currenttime}")
h.helicsPublicationPublishDouble(topicA, pi)
h.helicsFederateFinalize(fed)
h.helicsFederateFree(fed)
h.helicsCloseLibrary()
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with sender.json:
{
"coreType": "zmq",
"loglevel": 7,
"name": "sender",
"publications": [
{
"global": true,
"key": "topicA",
"required": true,
"type": "double"
}
],
"timeDelta": 1.0
}
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and we need a receiver.py:
# -*- coding: utf-8 -*-
import os
import helics as h
fed = h.helicsCreateCombinationFederateFromConfig(
os.path.join(os.path.dirname(__file__), "receiver.json")
)
topicA = h.helicsFederateGetSubscription(fed, "topicA")
h.helicsFederateEnterExecutingMode(fed)
currenttime = 0
for t in range(5, 10 + 1):
while currenttime < t:
currenttime = h.helicsFederateRequestTime(fed, t)
a = h.helicsInputGetDouble(topicA)
print(f"Received a = {a} at time = {currenttime}")
h.helicsFederateFinalize(fed)
h.helicsFederateFree(fed)
h.helicsCloseLibrary()
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and receiver.json:
{
"coreType": "zmq",
"loglevel": 7,
"name": "receiver",
"subscriptions": [
{
"global": true,
"key": "topicA",
"required": true,
"type": "double"
}
],
"timeDelta": 1.0
}
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You'll also need to run helics_broker in a separate window.
helics_broker -f 2
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# Output
This is the output of sender.py and receiver.py.
Sender.py
Sending value = 3.141592653589793 at time = 5.0
Sending value = 3.141592653589793 at time = 6.0
Sending value = 3.141592653589793 at time = 7.0
Sending value = 3.141592653589793 at time = 8.0
Sending value = 3.141592653589793 at time = 9.0
Sending value = 3.141592653589793 at time = 10.0
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Receiver.py
Received a = 0.0 at time = 5.0
Received a = 3.141592653589793 at time = 6.0
Received a = 3.141592653589793 at time = 7.0
Received a = 3.141592653589793 at time = 8.0
Received a = 3.141592653589793 at time = 9.0
Received a = 3.141592653589793 at time = 10.0
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You'll notice receiver.py received value 0.0 at time 5.0.
This is because receiver.py made a request to move to time 5.0 and was granted that time.