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A class DiffOp represents many common difference operators:
>>> from truncation_errors import DiffOp
>>> from sympy import *
>>> u = Symbol('u')
>>> diffop = DiffOp(u, independent_variable='t')
>>> diffop['geometric_mean']
-D1u**2*dt**2/4 - D1u*D3u*dt**4/48 + D2u**2*dt**4/64 + ...
>>> diffop['Dtm']
D1u + D2u*dt/2 + D3u*dt**2/6 + D4u*dt**3/24
>>> diffop.operator_names()
['geometric_mean', 'harmonic_mean', 'Dtm', 'D2t', 'DtDt',
'weighted_arithmetic_mean', 'Dtp', 'Dt']
Names in diffop:
Dtp for \( D^+_t \), Dtm for \( D_t^- \), Dt for \( D_t \), D2t for
\( D_{2t} \), DtDt for \( D_tD_t \).
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