Differences Between Arrays and Matrices in Numpy

What are some differences between arrays and matrices using the Numpy library? When would I want to use arrays instead of matrices and vice versa? -- http://mail.python.org/mailman/listinfo/python-list

Internal Math Library of Numpy

Does Numpy use Python's standard math library when calculating elementary functions such as exp(x) and acos(x)? Also, what is the internal library of Numpy and Python's standard math library? Is it platform independent? -- http://mail.python.org/mailman/listinfo/python-list