Sum PostgreSQL arrays in place [1,2,3] + [2,3,4] = [3,5,7]

AXH_Vector_Sum.sql

CREATE AGGREGATE vector_sum (
    sfunc = AXH_Vector_Sum,
    basetype = int[],
    stype = int[],
    initcond = '{0}'
);

DROP FUNCTION IF EXISTS AXH_Vector_Sum(int[], int[]);
CREATE OR REPLACE FUNCTION AXH_Vector_Sum(int[], int[]) 
    RETURNS int[] AS $$
    DECLARE 
        arr1 ALIAS FOR $1;
        arr2 ALIAS FOR $2;
        ina int[];
        inb int[];
        arr1n int := array_length(arr1, 1);
        arr2n int := array_length(arr2, 1);
    BEGIN
        --tbl := --our raster table name
        IF arr1n < arr2n THEN
            ina := arr2;
            inb := arr1;
        ELSE
            ina := arr1;
            inb := arr2;
        END IF;
        
        FOR i in array_lower(inb, 1) .. array_upper(inb, 1) LOOP
            ina[i] := ina[i] + inb[i];
        END LOOP;
        
        RETURN ina;
    END;
    $$ LANGUAGE 'plpgsql';
    
SELECT AXH_Vector_Sum('{1,2,3,2,1}'::int[], '{7,2,3,2,1}'::int[]);