I made a lot of progress and I think the code is almost finished, but
I have some troubles and need some reviews, to be sure that the
implementation goes on the right way. Should I open an issue to show
the code I made until yet?
I have some problems to simplify expression:
>>> a = Symbol('a')
>>> T = 3.155815e7*s
>>> M = 1.988435e30*kg
>>> aa = solve(T**2/a**3 - 4*pi**2 / G / M, a)
>>> res = aa[1].evalf()
>>> res
149598206033.591*kg**-1/3*kg**1/3*m*s**-2/3*s**2/3
>>> res.args
(149598206033.591, kg**-1/3, kg**1/3, m, s**-2/3, s**2/3)
>>> type(res)
<class 'sympy.core.mul.Mul'>
Harold
On 26 avr, 12:00, Harold Erbin <[email protected]> wrote:
> H Ondrej,
>
> Le dimanche 25 avril 2010 à 16:10 -0700, Ondrej Certik a écrit :
>
>
>
> > Hi Harold,
>
> > On Sun, Apr 25, 2010 at 3:52 AM, Harold E. <[email protected]> wrote:
> > > Hi,
>
> > > I saw that a new modules for physics began to be implemented, and the
> > > part which interested me was on the physicalunits: for a project I
> > > tried to write my own classes, inspired by those in ScientificPython,
> > > but evidently it was not compatible with sympy, and so I thought and
> > > tried to inspired from the classes in sympycore, without successes.
> > > But yet, with a better understanding of sympy, I read the recent
> > > implementation and had few questions and observations: the actual way
> > > is useful to make symbolic computations withunits, but it is
> > > convenient when we want to work withunits, e.g. to convert a quantity
> > > in one unit into another, or to take into account the dimension of
> > >units.
> > > So I was wondering me if it was not possible to merge actual and
> > > ScientificPython approaches. For my project I tried several ways, the
> > > latest was to create classes for the dimension (a tuple), the unit
> > > symbol (like actual unit) and for the unit; the latest having a
> > > symbol, a factor and a dimension — something like that (I still search
> > > the best way to arrange).
>
> > Is this how ScientificPython does it?
>
> >http://dirac.cnrs-orleans.fr/ScientificPython/ScientificPythonManual/...
>
> Yes, ScientificPython has two classes: one which handlesunitsand
> another for quantities. The Unit class has some properties like a
> dimension: e.g. for the meter has [1,0,0,0,0,0,0,0,0] and the joule
> [2,1,-2,0,0,0,0,0,0], and so on. They have also a factor (1 for meter,
> 1000 for km…) and of course a name. They can also have an offset (to
> symbolize degree Celsius for example). A quantity has a value and an
> unit.
> Several methods tests ifunitsare compatible, converts them into
> another… When operations are made betweenunits, a new unit is created
> from dimensions and factors.
>
> > Ourunitsare very simple, see sympy/physics/units.py, so anything
> > more advanced is welcomed. If you get something working, let us know
> > and we can review the code and merge it in, or help you improve it.
>
> > Ondrej
>
> I will try to make something good to submit it to you.
>
> The first approach I had was to directly make operations when twounits
> where together, but it gave strange comportment (even if, written on
> paper its more logic, it's not convenient for computing use, I think)
> like>>> m + m
> m
> >>> 1*m + 1*m
>
> 2*m
> so I try another way.
>
> I created a class Unit which have almost the same attributs as those in
> ScientificPython, but also a base symbol (like m for all distances),
> which is used when computations are made. It will have the methods to
> convertunits. This class does not inherit from another class, but the
> class for the symbol is the same as those defined in the actualunits.py
> from sympy. I made also a short class for the Dimension.
> The main problems after is how transform an object like Mul, Add…
> (passed in argument) into a Quantity (I did not already read the
> documentation for that), which have methods to change itsunits…
>
> How can I show you the code? Should I create a new issue on tracker and
> attach the code?
>
> I had a problem with the code in sympy/physics/units.py (0.6.7 version
> or svn): when I use the class Unit like it is defined, it works fine:>>> m =
> Unit('meter', 'm')
> >>> m
>
> m
> but if I rename it into UnitSymbol, I have:>>> m = UnitSymbol('meter', 'm')
> >>> m
>
> UnitSymbol()
>
> Do you know how I can fit that? I try to search into the code, but I did
> not see anything which can help me.
>
> Harold
>
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