Update :
For the moment with a 10x10 symbolic array, I tried (in a first decrease all the 2 indices from 1) :
a=sym('a_',[10,10])
array_a=char(a)
regexprep(array_a,'a_\D_\D', 'a_eval(\D-1_\D-1)')
but indices are not decreased from 1 :
'[a_1_1, a_1_2, a_1_3, a_1_4, a_1_5, a_1_6, a_1_7, a_1_8, a_1_9, a_1_10; a_2_1, a_2_2, a_2_3, a_2_4, a_2_5, a_2_6, a_2_7, a_2_8, a_2_9, a_2_10; a_3_1, a_3_2, a_3_3, a_3_4, a_3_5, a_3_6, a_3_7, a_3_8, a_3_9, a_3_10; a_4_1, a_4_2, a_4_3, a_4_4, a_4_5, a_4_6, a_4_7, a_4_8, a_4_9, a_4_10; a_5_1, a_5_2, a_5_3, a_5_4, a_5_5, a_5_6, a_5_7, a_5_8, a_5_9, a_5_10; a_6_1, a_6_2, a_6_3, a_6_4, a_6_5, a_6_6, a_6_7, a_6_8, a_6_9, a_6_10; a_7_1, a_7_2, a_7_3, a_7_4, a_7_5, a_7_6, a_7_7, a_7_8, a_7_9, a_7_10; a_8_1, a_8_2, a_8_3, a_8_4, a_8_5, a_8_6, a_8_7, a_8_8, a_8_9, a_8_10; a_9_1, a_9_2, a_9_3, a_9_4, a_9_5, a_9_6, a_9_7, a_9_8, a_9_9, a_9_10; a_10_1, a_10_2, a_10_3, a_10_4, a_10_5, a_10_6, a_10_7, a_10_8, a_10_9, a_10_10]'
Remains also after this operation the inverse operation of char, i.e convert string to symbolic matrix array.
Does anybody see a solution ?