An array variable references a dynamic or dimensioned array.
When an array variable is used to describe a dimensioned array, it must be used with a subscript to indicate the specific variable descriptor in the array:
a(10) or a(n)
Otherwise it must be used in a mat statement to indicate all elements in the array:
mat a = ''
This sets every variable in the array a to null.
matread afrom...
This reads an item and parses the attributes to the dimensioned array a.