Array Conformability Rules Operands may be arrays, in which case
the operation is performed on each element of the array(s) to
produce an array result. Binary operands need not have identical
dimensions, but their dimensions must be conformable. Two arrays
are conformable if their first dimensions match, their second
dimensions match, their third dimensions match, and so on up to
the number of dimensions in the array with the fewer dimensions.
Two array dimensions match if either of the following conditions
is met: Unit length or missing dimensions are broadcast (by
copying the single value) to the length of the corresponding
dimension of the other operand. The result of the operation has
the number of dimensions of the higher rank operand, and the
length of each dimension is the longer of the lengths in the two
operands.