Fibonacci Triangle Matrices

[compsystems]

The FIBMAT() current code only works in numerical mode (HOME), but it must be taken into account that if the index variable that can only be changed in CAS mode, is in 'index': = 0, it affects the output of the function


test
Steps:
1: Press [CAS]
2: index:=0 [↵] returns "[] index start 0"
3: then Press [HOME]
4: FIBMAT(7) [↵]
[[1,0,0,0,0,0,0,0],[1,1,0,0,0,0,0,0],[1,1,2,0,0,0,0,0],[1,1,2,3,0,0,0,0],[1,1,2,3,5,0,0,0],[1,1,2,3,5,8,0,0],[1,1,2,3,5,8,13,0],[1,1,2,3,5,8,13,21]]


5: Press [CAS]
6: index:=1 [↵] returns "[] index start 1"
7: then Press [HOME]
8: FIBMAT(7) [↵]
[[1,0,0,0,0,0,0,0],[1,1,0,0,0,0,0,0],[2,1,2,0,0,0,0,0],[3,2,2,3,0,0,0,0],[5,3,4,3,5,0,0,0],[8,5,6,6,5,8,0,0],[13,8,10,9,10,8,13,0],[21,13,16,15,15,16,13,21]]


I try to change the value of the internal variable within the code but it fails.
CAS.index:=1;

PHP Code:

EXPORT FIBMAT(n)
BEGIN
// Fibonacci "triangle" in
// matrix form
// 2018-12-17 EWS
LOCAL M1,k;
CAS.index:=1;

M1:=MAKEMAT(0,n+1,n+1);
M1(1,1):=1;
M1(2,1):=1;
M1(2,2):=1;
FOR k FROM 3 TO n+1 DO
M1(k):=row(M1,k-1)+row(M1,k-2);
M1(k,k):=M1(k-1,k-1)+M1(k-2,k-2);
END;
RETURN M1;
END;