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TODO List, mostly historical now

assumptions

http://docs.sympy.org/dev/modules/assumptions/assume.html

You can define integers at creation:

x, y, z, t = symbols('x y z t') k, m, n = symbols('k m n', integer=True) f, g, h = symbols('f g h', cls=Function)

x = Symbol('x', real=True, positive=True)

In Matlab's SMT, assumptions effect expressions already defined. This seems a bit at odds with Sympy (also c.f., global_assumptions). The easier approach is to put them in Symbol()

Global assumptions don't apply "automatically"?

from sympy.assumptions.assume import global_assumptions from sympy import Q GA = global_assumptions x = sp.Symbol('x')

In [23]: sp.sqrt(x2) Out[23]: sqrt(x2)

GA.add(Q.positive(x))

In [29]: sp.sqrt(x2) Out[29]: sqrt(x2)

In [31]: sp.refine(sp.sqrt(x**2)) Out[31]: x

Assumptions on variables in the constructor

This works well. But how to map this onto the assume() and alsoAssume() commands? Proposal: set assume to generate help text and a warning. And extend the constructor instead to work like sympy...

equality

MST: ==, define equations, equality test only when both sides become double SymPy: relationalequality, eq()

MST: logical(), "structural" equivalence SymPy: ==

MST: isAlways(), "mathematical" equivalence SymPy: bool(LHS.expand() == RHS.expand())

If .expand() does not help, try simplify(), trigsimp(), etc, which attempt more advanced transformations. For example, [https://github.com/sympy/sympy/wiki/Faq]

matrices

Fundamental choice: (1) make a matrix array of sym objects; or (2) use sp.Matrix in sympy.

(1+) seems easy to start with (1-) but then sin(x) for example will need to call sin for each entry

(2-) requires some effort for functions: A.applyfunc(sp.sin) (2+) renders nicely already

essential issue is that scalars are not (1,1) matrices in sympy. Could do that but, e.g., diff might not work... well we could just generate the code to make it work.

IPC

Currently we have two approaches implemented:

  • Using system()

  • Using popen2()

There are quite a few options out there:

Limitations of system()

We used to create a temporary file and execute it with system(). But its nicer to pass the command itself on the command line with "python -c". IIRC, I couldn't make this work with multiline pickles (i.e., most of them).