> ## Documentation Index
> Fetch the complete documentation index at: https://doc.blueapi.ir/llms.txt
> Use this file to discover all available pages before exploring further.

# Tensor Shape Validation Algorithm and Rules

> Tensor shape validation specification for EMEP. Iterates over state_dict, compares shapes and dtypes per parameter, reports first mismatch, and references broadcasting rules from Tensor Math.

Tensor shape validation is the final gate before a merge can proceed. This page specifies the algorithm that iterates over state\_dict entries, compares shapes and dtypes, and reports the first fatal mismatch.

## Validation Algorithm

```mermaid theme={null}
flowchart TD
    START([START]) --> INPUT[Input: Model A state_dict + Model B state_dict]
    INPUT --> KEYS{Key sets equal?}
    KEYS -->|no| DIFF[Compute key difference]
    DIFF --> ONLY_A{Keys only in A?}
    ONLY_A -->|yes| INCOMPATIBLE_1[INCOMPATIBLE: parameter set mismatch]
    ONLY_A -->|no| ONLY_B{Keys only in B?}
    ONLY_B -->|yes| INCOMPATIBLE_1
    ONLY_B -->|no| ITER[Iterate over shared keys]
    KEYS -->|yes| ITER
    ITER --> SHAPE{Shape match?}
    SHAPE -->|no| REPORT[Report mismatch: key, expected, actual]
    REPORT --> INCOMPATIBLE_2[INCOMPATIBLE: shape mismatch]
    SHAPE -->|yes| DTYPE{dtype compatible?}
    DTYPE -->|no| CONDITIONALLY_COMPATIBLE[CONDITIONALLY_COMPATIBLE: dtype mismatch]
    DTYPE -->|yes| NEXT{More keys?}
    NEXT -->|yes| ITER
    NEXT -->|no| COMPATIBLE[COMPATIBLE]
    COMPATIBLE --> END([END])
    CONDITIONALLY_COMPATIBLE --> END
    INCOMPATIBLE_1 --> END
    INCOMPATIBLE_2 --> END
```

## Dtype Compatibility Rules

| Dtype A | Dtype B | Compatible?               | Action if CONDITIONALLY\_COMPATIBLE |
| ------- | ------- | ------------------------- | ----------------------------------- |
| fp32    | fp32    | Yes                       | None                                |
| fp32    | bf16    | CONDITIONALLY\_COMPATIBLE | Cast to fp32 or bf16                |
| fp32    | fp16    | CONDITIONALLY\_COMPATIBLE | Cast to fp32 or fp16                |
| bf16    | bf16    | Yes                       | None                                |
| bf16    | fp16    | CONDITIONALLY\_COMPATIBLE | Cast to fp32                        |
| fp16    | fp16    | Yes                       | None                                |
| int8    | int8    | Yes                       | None                                |
| int8    | fp16    | CONDITIONALLY\_COMPATIBLE | Dequantize or quantize              |
| int4    | int4    | Yes                       | None                                |
| int4    | any     | CONDITIONALLY\_COMPATIBLE | Dequantize                          |

## Broadcasting Rules

When shapes do not match exactly, the TensorEngine applies broadcasting rules defined in [Tensor Math](/math/tensor-math). Broadcasting is only permitted when the shapes are compatible per elementwise rules: dimensions must be equal or one of them must be 1. Broadcasting across parameter keys (e.g., different layer counts) is not supported and produces INCOMPATIBLE.

## Mismatch Report Format

The first mismatch terminates validation and produces a structured report:

```json theme={null}
{
  "status": "INCOMPATIBLE",
  "key": "model.layers.0.self_attn.q_proj.weight",
  "expected_shape": [4096, 4096],
  "actual_shape": [4096, 5120],
  "expected_dtype": "float32",
  "actual_dtype": "float32"
}
```

## Cross-Links

* [Model Compatibility](/compatibility/model-compatibility) for the full decision tree.
* [Architecture Compatibility](/compatibility/architecture-compatibility) for architecture checks.
* [Tensor Math](/math/tensor-math) for broadcasting and elementwise rules.
* [Merge Engine](/merge/merge-engine) for how validation feeds into merging.