Bug in propagation algorithm for updates

[Rex-8]

Bounty Points: 150

Branch Instructions

push changes to a new 'propogation' branch

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Explanation:

• num_of_cars() function incorrectly calculates car redistribution
• Only counts incoming cars from one edge instead of all incoming edges
• Logic error: uses cars_initial[node] when should use source node count
• Distribution ratios applied incorrectly
• Causes negative car counts and simulation errors

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Current buggy code:

def num_of_cars(node):
    t = 0
    for i in distances:
        if i[1] == node:
            for j in distribution:
                if j == i[0]:
                    for k in distribution[j]:
                        if k[0] == node:
                            t += (cars_initial[node]) * k[1]  # BUG: wrong node
    t -= (distribution[node][0][1]) * (cars_initial[node])
    cars_initial[node] = t
    return t

Possible fix/approach:

• For each edge (source -> target) where target == node:
  • Add cars_initial[source] * distribution[source][target_ratio]
• Calculate outgoing cars separately
• Formula: new_count = current + incoming - outgoing
• Ensure non-negative car counts
• Fix global state mutation issue

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Correct logic (Example):

incoming = sum(cars_initial[src] * ratio
                for edge in distances if edge[1] == node
               for src, ratio in get_incoming_ratio(edge[0], node))
outgoing = sum(cars_initial[node] * ratio
                for dest, ratio in distribution[node] if dest != node)

Maintainer notes:

• Critical bug affecting entire simulation accuracy
• Test with simple 2-3 node graphs first
• Verify car conservation (total cars should remain constant)
• Check distribution ratios sum to 1.0

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Resources:

• Traffic flow conservation principles
• Graph theory: flow networks

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[JagritiM123]

i would like to be assigned to this issue

[Mayur-Shashidhar]

I will take this

[balaraj74]

can i get assigne for this

[Pratham042006]

FCFS will be followed for minor issues

!assign @JagritiM123

[Pratham042006]

!assign @JagritiM123

[ananyaasp]

assign to me pls

[hasithsreeram]

Can i get assigned for this ?

[JagritiM123]

please re-assign again

[bunsamosa-bot]

Hey @Pratham042006! The timer for the @JagritiM123 to work on the issue has finished, deassign and assign a new contributor or extend the current timer. Contact maintainer leads if inactive @mebinthattil @adityatr64