Here's a possible way to solve the precision problems with Maxima. This
replaces RealNumbers and RealLiterals with variables before simplifying an
Expression.
from sage.symbolic.expression_conversions import Converter
class DoNothing(Converter):
def arithmetic(self, ex, operator):
return reduce(operator, map(self, ex.operands()))
def pyobject(self, ex, obj):
return ex
def symbol(self, ex):
return ex
def relation(self, ex, operator):
return operator(*map(self, ex.operands()))
def derivative(self, ex, operator):
#We'll just ignore this for now
return ex
def composition(self, ex, operator):
return operator(*map(self, ex.operands()))
class MaintainPrec(DoNothing):
def __init__(self):
self.repl_dict = {}
self.counter = 1
def pyobject(self, ex, obj):
if isinstance(obj, sage.rings.real_mpfr.RealLiteral) or
isinstance(obj, sage.rings.real_mpfr.RealNumber):
newvar = var('repl%s' % self.counter)
self.repl_dict[newvar] = obj
self.counter += 1
return newvar
else:
return obj
def safe_simplify(expr):
replacer = MaintainPrec()
return replacer(expr).simplify_full().subs(replacer.repl_dict)
Now:
sage: a = RealField(200)(8.987551787368175506591796875e9)
sage: var('y')
y
sage: b = (a * x).mul(y, hold=True)
sage: (b / (x * y)).simplify()
8987551787.37
sage: safe_simplify(b / (x * y))
8.9875517873681755065917968750000000000000000000000000000000e9
Does this look like a good solution? It should be done before sending any
Expression to Maxima, because Maxima itself does not try to preserve
precision at all with its
bigfloats<http://trac.sagemath.org/sage_trac/ticket/11643#comment:3>
.
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