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@manyasha-n-m @Pavlo3P @alnaba1 I've implemented G constraint and merged it into the master branch. You can use it as a template, but don't hesitate to ask me if you need some further clarification.

@PaulWAyers I assume that number of electrons is given by user, but do you thing, I should compute from DM directly inside the function? Implementation is here

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The number of electrons can be given by the user or inferred from the density matrix. I would allow it as an optional argument; if it is not given then the density matrix is used to infer the number of electrons. If the number of electrons is given, then this affects the value of the trace one is enforcing.

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So if n == None then:
you would compute.

Note that by pep8 standards I am pretty sure that n should be lower case. Might be better to name it n_el or n_e just to be clearer.

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