working-with-compositions.rst

Working with compositions

The simplest entity in hydrosolver is Composition. Compositions can be defined on the go or loaded from a file, added and scaled.

Defining a composition

The most straightforward way to define a compostion is using its constructor Composition(name, vector). The simplest composition which does not contain any of the nutrient elements of our interest would be Composition(name='Pure water').

The monopotassium phosphate can be defied as follows:

>>> from hydrosolver.composition import Composition >>> MKP = Composition( ... name='Monopotassium phosphate', ... vector=[0, 0, 0.2276, 0.2873, 0, 0, 0, 0, 0, 0, 0, 0, 0], ... ) >>> MKP Composition: Monopotassium phosphate <BLANKLINE> Nutrient Ratio Amount mg/kg ---------- ------- --------------P 0.2276 227600 K 0.2873 287300

Here vector follows the structure of composition.nutrients_stencil. Let us check the result.

It is hard to not notice that this kind of definition is cumbersome and can be barely used by humans. Therefore class Composition contains an alternative constructor Composition.from_dict(), so the same result could be achieved in the following way:

>>> MKP = Composition.from_dict( ... {'Monopotassium phosphate': {'P': 0.2276, 'K': 0.2873}} ... ) >>> MKP Composition: Monopotassium phosphate <BLANKLINE> Nutrient Ratio Amount mg/kg ---------- ------- --------------P 0.2276 227600 K 0.2873 287300

Loading and dumping compositions

It makes sense to save frequently used composition into a database and further load it from there. Here is an example:

import yaml

with open('database.yaml', 'w') as database:
    database.write(yaml.dump(MKP.as_dict()))

Multiple compositions can be loaded at once from a file:

from hydrosolver.utils import load_file

compositions = load_file('compositions/pure.yaml')

Operations on compositions

Compositions can be added and scaled, i.e. multiplied by scalars. You will typically not need to add or subtract compositions, but consider the following use case for scaling:

>>> KOH = Composition.from_dict( ... {'Potassium hydroxide': {'K': 0.69687}} ... ) >>> KOH_94 = 0.94 * KOH >>> KOH_94 Composition: 0.94 * (Potassium hydroxide) <BLANKLINE> Nutrient Ratio Amount mg/kg ---------- -------- --------------K 0.655058 655058