Changes implementation to SymPy

[schymans]

Use of MKS in https://github.com/environmentalscience/essm/blob/sympy/essm/variables/units.py#L58 is not adequate, as MKS stands for "meter, kilogram, second". We also need representations for kelvin and mole, others might also need ampere and candela etc.

[jirikuncar]

@schymans can we use the natural system?

[schymans]

No, sorry, natural is even worse:

>>> from essm.variables.units import MKS
>>> quantities = [T_a, nu_a, p_nua1, p_nua2]
>>> print [a.convert_to(MKS.print_unit_base(a)) for a in quantities]
[T_a, meter**2/second, p_nua1, meter**2/second]

This one only fails on T_a, but natural returns useless stuff:

>>> from sympy.physics.units.systems import natural
>>> quantities = [T_a, nu_a, p_nua1, p_nua2]
>>> print [a.convert_to(natural.print_unit_base(a)) for a in quantities]
[T_a, 0.0169042576289485*hbar*speed_of_light**2/electronvolt, p_nua1, 0.0169042576289485*hbar*speed_of_light**2/electronvolt]

We may have to write an additional units system called SI.

[schymans]

MKSA only adds ampere. I created SI, based on MKSA with a complete set of SI base units (i.e. adding K, mol and cd). I will try to also create a PR on SYMPY to include it.

On 07/06/2017 10:15 AM, Jiri Kuncar wrote:

@schymans https://github.com/schymans can we use the MKSA (https://github.com/sympy/sympy/blob/1.1/sympy/physics/units/systems/mksa.py#L32)?

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