On Sun, Feb 5, 2012 at 11:54 AM, Comer <comer.dun...@gmail.com> wrote:
> I am working on a project which requires that I create a matrix of
> symbols. For discussion purposes say the matrix is 3 x 3. The matrix
> is to contain 9 unique symbols and my preferred format is the usual
> matrix format:
>
> a11, ..., a33 = symbols('a_11 ....a_33')
>
> Now obviously I could easily just type in the above for all nine
> symbols. However, what I want to see how to do is to create a 3 x 3
> array as above but do it in a couple of for loops. I looked at the
> symbols() function but it only seems to work with a linear sequence of
> symbol names such as x0, x1, x2, .... xN. But I can not see how to do
> the same for a 2d array of symbol names such as x00, x01, x02, ... .
> It would be convenient in my project to be able to quickly create the
> 2d array of symbols directly by calling symbols(). It would save some
> typing.
>
> Can someone please let me know how best to do this?
I think you are looking for the symarray() function in sympy:
Type: function
Base Class: <type 'function'>
String Form:<function symarray at 0x2aa3488>
Namespace: Interactive
File: /home/ondrej/repos/sympy/sympy/matrices/matrices.py
Definition: symarray(prefix, shape)
Docstring:
Create a numpy ndarray of symbols (as an object array).
The created symbols are named `prefix_i1_i2_`... You should thus provide a
non-empty prefix if you want your symbols to be unique for different output
arrays, as Sympy symbols with identical names are the same object.
Parameters
----------
prefix : string
A prefix prepended to the name of every symbol.
shape : int or tuple
Shape of the created array. If an int, the array is one-dimensional; for
more than one dimension the shape must be a tuple.
Examples
--------
These doctests require numpy.
>>> from sympy import symarray
>>> symarray('', 3) #doctest: +SKIP
[_0, _1, _2]
If you want multiple symarrays to contain distinct symbols, you *must*
provide unique prefixes:
>>> a = symarray('', 3) #doctest: +SKIP
>>> b = symarray('', 3) #doctest: +SKIP
>>> a[0] is b[0] #doctest: +SKIP
True
>>> a = symarray('a', 3) #doctest: +SKIP
>>> b = symarray('b', 3) #doctest: +SKIP
>>> a[0] is b[0] #doctest: +SKIP
False
Creating symarrays with a prefix:
>>> symarray('a', 3) #doctest: +SKIP
[a_0, a_1, a_2]
For more than one dimension, the shape must be given as a tuple:
>>> symarray('a', (2, 3)) #doctest: +SKIP
[[a_0_0, a_0_1, a_0_2],
[a_1_0, a_1_1, a_1_2]]
>>> symarray('a', (2, 3, 2)) #doctest: +SKIP
[[[a_0_0_0, a_0_0_1],
[a_0_1_0, a_0_1_1],
[a_0_2_0, a_0_2_1]],
<BLANKLINE>
[[a_1_0_0, a_1_0_1],
[a_1_1_0, a_1_1_1],
[a_1_2_0, a_1_2_1]]]
Ondrej
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