### broadcasting rule

ncnn BinaryOp accepts blobs with different shape

C = BinaryOp(A, B)

shape notation convention is [w], [w,h], [w,h,c]

|type|A|B|C|
|---|---|---|---|
|1|[1]|scalar|[1]|
|2|[1]|[1]|[1]|
|3|[1]|[2,3]|[2,3]|
|4|[1]|[2,3,4]|[2,3,4]|
|5|[2]|scalar|[2]|
|6|[2]|[1]|[2]|
|7|[2]|[2]|[2]|
|8|[3]|[2,3]|[2,3]|
|9|[4]|[2,3,4]|[2,3,4]|
|10|[2,3]|scalar|[2,3]|
|11|[2,3]|[1]|[2,3]|
|12|[2,3]|[3]|[2,3]|
|13|[2,3]|[2,3]|[2,3]|
|14|[3,4]|[2,3,4]|[2,3,4]|
|15|[2,3,4]|scalar|[2,3,4]|
|16|[2,3,4]|[1]|[2,3,4]|
|17|[2,3,4]|[4]|[2,3,4]|
|18|[2,3,4]|[3,4]|[2,3,4]|
|19|[2,3,4]|[2,3,4]|[2,3,4]|

some special broadcasting rule exists for model compatibility

|special type|A|B|C|
|---|---|---|---|
|1|[2,3,4]|[1,1,4]|[2,3,4]|