Plus and minus for an array would have their normal meaning. However, multiplication and division have quite different definitions. Using multiplication as an example, A × B arrays could have two meanings: either item by item (A and B should have the same dimensions, that is, both are n by m) or matrix multiplication (the second dimension of A should be the same as the first dimension of B, that is, A is n by m while B is m by p ).
When adding or subtracting two arrays, they must have the same dimensions, that is, both are n by m. If they have different dimensions, we will get an error message. The following example shows the summation of two cash flow arrays:
>>>cashFlows_1=np.array([-100,50,20]) >>>cashFlows_2=np.array([-80,100,120]) >>>cashFlows_1 + cashFlows_2 >>>array([-180, 150, 140])