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18650 series-parallel battery-pack co-design grammar
====================================================

A constrained grammar for repositioning 18650 cells and editing whole series stages or parallel branches in a rectangular SxP battery pack.

See :doc:`../grammar` for the grammar family index.

Quick Facts
-----------

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   * - Field
     - Value
   * - Problem ID
     - ``battery_pack_18650_series_parallel``
   * - Problem Family
     - grammar
   * - Implementation
     - ``design_research_problems.problems.grammar._battery_pack_sp:BatteryPack18650SeriesParallelProblem``
   * - Capabilities
     - ``discrete-actions``, ``external-adapter``, ``optional-evaluator``, ``serializable-state``, ``statement-markdown``
   * - Study Suitability
     - none
   * - Tags
     - ``grammar``, ``battery``, ``series-parallel``, ``layout``, ``co-design``

Taxonomy
--------

Formulation
   discrete_grammar
Convexity
   not_applicable
Design Variable Type
   discrete
Is Dynamic
   no
Orientation
   engineering_practical
Feasibility Ratio Hint
   0.1
Objective Mode
   multi
Constraint Nature
   hard
Bounds Summary
   explicit 3D cell coordinates inside a fixed envelope with a complete SxP topology
Tags
   ``grammar``, ``battery``, ``series-parallel``, ``layout``, ``co-design``

Statement
---------

Design a battery pack using 18650 cells under a constrained series-parallel topology. The pack always forms a complete rectangular grid of logical electrical slots: ``S`` series stages by ``P`` parallel branches, with exactly one physical cell per slot. Designers may reposition cells in space, add a full new series stage, remove the final series stage, add a full new parallel branch, or remove the final parallel branch.

The benchmark target is a ``14.8V`` pack with at least ``10Ah`` capacity and at least ``60A`` continuous current, under a ``500mm x 500mm x 250mm`` envelope. Evaluation uses deterministic geometry and coarse thermal checks plus an optional PyBaMM-backed representative-cell discharge simulation.

Problem Shape
-------------

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   * - Field
     - Value
   * - State Type
     - SeriesParallelBatteryState
   * - Initial Transition Count
     - 21
   * - Initial Rule Names
     - ``add_parallel_branch``, ``add_series_stage``, ``move_cell``

Manifest Parameters
-------------------

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   * - Key
     - Value
   * - max_depth_mm
     - 500
   * - max_height_mm
     - 250
   * - max_width_mm
     - 500
   * - minimum_capacity_ah
     - 10
   * - minimum_current_a
     - 60
   * - target_voltage_v
     - 14.8
   * - voltage_tolerance_v
     - 0.1

Initial Transition Summary
--------------------------

.. list-table::
   :header-rows: 1
   :widths: 70 30

   * - Rule Name
     - Transition Count
   * - add_parallel_branch
     - 7
   * - add_series_stage
     - 7
   * - move_cell
     - 7

Library Interface
-----------------

- ``initial_state()``
- ``enumerate_transitions(state)``
- ``enumerate_next_states(state)``
- ``evaluate(state)``