Re: Differences Between Arrays and Matrices in Numpy
On 2009-07-29 18:27, Colin J. Williams wrote: Robert Kern wrote: On 2009-07-29 15:23, Nanime Puloski wrote: 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? You will want to ask numpy questions on the numpy mailing list: http://www.scipy.org/Mailing_Lists An overview of how the matrix subclass differs from ndarray, see the documentation: http://docs.scipy.org/doc/numpy/reference/arrays.classes.html#matrix-objects Basically, I suggest that you just use regular arrays always. There is a syntactical convenience to matrix objects, but it does cause incompatibilities with the majority of code that is written for regular arrays. The convenience is usually not worth the cost. Numpy's arrays can have any dimensionality, whereas matrices[http://en.wikipedia.org/wiki/Matrix_%28mathematics%29], typically have two. A single column can represent a vector or a single row can represent a transposed vector. Does the additional cost arise because the commonly used procedures are accessed through numpy's array? Most functions are written to expect that its inputs behave like ndarrays; e.g. a*b is elementwise multiplication rather than matrix multiplication. When you use the matrix subclass, you are basically confining yourself to a smallish ghetto of functions that knows how to deal with matrix semantics. That's a huge cost compared to the relatively small syntactic cost of having to write dot(a,b) instead of (a*b). -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
Re: Differences Between Arrays and Matrices in Numpy
Robert Kern wrote: On 2009-07-29 15:23, Nanime Puloski wrote: 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? You will want to ask numpy questions on the numpy mailing list: http://www.scipy.org/Mailing_Lists An overview of how the matrix subclass differs from ndarray, see the documentation: http://docs.scipy.org/doc/numpy/reference/arrays.classes.html#matrix-objects Basically, I suggest that you just use regular arrays always. There is a syntactical convenience to matrix objects, but it does cause incompatibilities with the majority of code that is written for regular arrays. The convenience is usually not worth the cost. Numpy's arrays can have any dimensionality, whereas matrices[http://en.wikipedia.org/wiki/Matrix_%28mathematics%29], typically have two. A single column can represent a vector or a single row can represent a transposed vector. Does the additional cost arise because the commonly used procedures are accessed through numpy's array? Colin W. -- http://mail.python.org/mailman/listinfo/python-list
Re: Differences Between Arrays and Matrices in Numpy
On Wed, 29 Jul 2009 16:23:33 -0400, Nanime Puloski wrote: > What are some differences between arrays and matrices using the Numpy > library? Matrices are always two-dimensional, as are slices of them. Matrices override mulitplication and exponentiation to use matrix multiplication rather than element-wise multiplication. > When would I want to use arrays instead of matrices and vice > versa? Use a matrix if you want a matrix, i.e. a linear transformation. Otherwise, use an array. -- http://mail.python.org/mailman/listinfo/python-list
Re: Differences Between Arrays and Matrices in Numpy
On 2009-07-29 15:23, Nanime Puloski wrote: 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? You will want to ask numpy questions on the numpy mailing list: http://www.scipy.org/Mailing_Lists An overview of how the matrix subclass differs from ndarray, see the documentation: http://docs.scipy.org/doc/numpy/reference/arrays.classes.html#matrix-objects Basically, I suggest that you just use regular arrays always. There is a syntactical convenience to matrix objects, but it does cause incompatibilities with the majority of code that is written for regular arrays. The convenience is usually not worth the cost. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
