2d array issues

Hello,
Can anyone tell me why the function below is breaking at the second
assignment? I am trying to set values for columns 1 and 2 for row 1. The
compilation and error are below the function definition. Thanks in advance.

1. CREATE OR REPLACE FUNCTION test() returns void AS $$
2. declare
3. matrix numeric [][];
4. cnt numeric := 1;
5. begin
6. matrix[cnt][1] := 3;
7. raise notice '%', matrix[cnt][1];
8. matrix[cnt][2] := 4;
9. raise notice '%', matrix[cnt][2];
10. end;
11. $$ LANGUAGE plpgsql;
12.
13. error...
14. stocks=# \i test.sql
15. CREATE FUNCTION
16. stocks=# select test();
17. NOTICE: 3
18. ERROR: invalid array subscripts
19. CONTEXT: PL/pgSQL FUNCTION "test" line 7 at assignment