Yes, you can use an expression tree walker:
from sage.symbolic.expression_conversions import ExpressionTreeWalker
class SubstituteNumericalApprox(ExpressionTreeWalker):
def __init__(self, **kwds):
"""
A class that walks the tree and replaces numbers by numerical
approximations with the given keywords to `numerical_approx`.
EXAMPLES::
sage: var('F_A,X_H,X_K,Z_B')
sage: expr = 0.0870000000000000*F_A + X_H + X_K + 0.706825181105366*Z_B - 0.753724599483948
sage: SubstituteNumericalApprox(digits=3)(expr)
0.0870*F_A + X_H + X_K + 0.707*Z_B - 0.754
"""
self.kwds = kwds
def pyobject(self, ex, obj):
if hasattr(obj, 'numerical_approx'):
return obj.numerical_approx(**self.kwds)
else:
return obj
def __call__(self, ex):
result = super().__call__(ex)
return result.numerical_approx(**self.kwds) if result in CC else result
Example usage:
sage: var('F_A,X_H,X_K,Z_B')
sage: expr = 0.0870000000000000*F_A + X_H + X_K + 0.706825181105366*Z_B - 0.753724599483948
sage: SubstituteNumericalApprox(digits=3)(expr)
0.0870*F_A + X_H + X_K + 0.707*Z_B - 0.754
sage: SubstituteNumericalApprox(digits=5)(1.5*2^x/log(2))
2.1640*2.0000^x
A small improvement to the code proposed so as to prevent integers from being cast to float as I noticed that this was the case for me:
def pyobject(self, ex, obj):
if hasattr(obj, 'numerical_approx'):
if hasattr(obj, 'parent'):
if obj.parent()==sg.IntegerRing():
return obj
return obj.numerical_approx(**self.kwds)
else:
return obj
Asked: 2019-04-09 11:52:46 +0100
Seen: 1,001 times
Last updated: Jan 08 '22
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