K (ngn/k), 23 bytes

{x+x&2{++/'3'0,x,0}/~x}

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uses 0 1 2 for "AB+"

{ } function with argument x

~ logical not

2{ }/ twice do

• 0,x,0 surround with 0-s (top and bottom of the matrix)

• 3' triples of consecutive rows

• +/' sum each

• + transpose

x& logical and of x with

x+ add x to

K (ngn/k), 24 bytes

{x+x&2{++/'3':0,x,0}/~x}

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uses 0 1 2 for "AB+"

{ } function with argument x

~ logical not

2{ }/ twice do

• 0,x,0 surround with 0-s (top and bottom of the matrix)

• 3': triples of consecutive rows

• +/' sum each

• + transpose

x& logical and of x with

x+ add x to

K (ngn/k), 23 bytes

{x+x&2{++/'3'0,x,0}/~x}

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uses 0 1 2 for "AB+"

{ } function with argument x

~ logical not

2{ }/ twice do

• 0,x,0 surround with 0-s (top and bottom of the matrix)

• 3' triples of consecutive rows

• +/' sum each

• + transpose

x& logical and of x with

x+ add x to

K (ngn/k), 23 bytes

{x+x&2{++/'3'0,x,0}/~x}

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uses 0 1 2 for "AB+"

{ } function with argument x

~ logical not

2{ }/ twice do

• 0,x,0 surround with 0-s (top and bottom of the matrix)

• 3' triples of consecutive rows

• +/' sum each

• + transpose

x& logical and of x with

x+ add x to

K (ngn/k), 23 bytes

{x+x&2{++/'3'0,x,0}/~x}

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uses 0 1 2 for A, B, and +

{ } function with argument x

~x logical not

2{ }/ twice do

0,x,0 surround with 0-s (top and bottom)

3' triples of consecutive rows

+/' sum each

+ transpose

x& minima between x and

x+ add x to

K (ngn/k), 23 bytes

{x+x&2{++/'3'0,x,0}/~x}

Try it online!

uses 0 1 2 for "AB+"

{ } function with argument x

~ logical not

2{ }/ twice do

• 0,x,0 surround with 0-s (top and bottom of the matrix)

• 3' triples of consecutive rows

• +/' sum each

• + transpose

x& logical and of x with

x+ add x to