HP-71B Dynamic array allocation

[J-F Garnier]

The array allocation on the 71B is indeed dynamic, that is you can increase/decrease the size of the array with memory taken from/released to the free memory pool.

In other HP BASIC implementations, such as the 75C, Series 80 or RMB, the array is allocated only once (sometimes in the "pre-run" phase) with the DIM statement and constant (static) dimensions, i.e. DIM A(10,10) not N= 10 @ DIM A(N,N).
In these implementations, the REDIM statement can be used to change the array dimensions within the limits of the DIM memory allocation, and the elements are then preserved, with a significant difference versus the 71B:

HP-71B                     HP-75C
10 OPTION BASE 1           10 OPTION BASE 1
20 DIM A(3,3)              20 DIM A(3,3)
30 MAT A=(1)               30 MAT A=(1)
40 DIM A(2,2)              40 REDIM A(2,2)
50 DIM A(3,3)              50 REDIM A(3,3) 
60 MAT PRINT A;            60 MAT PRINT A;

1 1 1                      1 1 1
1 0 0                      1 1 1
0 0 0                      1 1 1

J-F
(from a hypothetical future "Lectures on HP BASIC" :-)