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How to avoid scientific notation of numbers in the Mathematica interface

asked 2019-11-27 09:30:46 -0600

bekalph gravatar image

I use the mathematica interface to compute numerical values of an extended hyper-geometric function MeijerG for real arguments. This function is provided only by Mathematica:

var('x,mx')
x=0.00001
resp=mathematica.set(mx,x)
mathematica('MeijerG[{{1, 3/2}, {}}, {{1, 1}, {1/2}}, mx]')

For real arguments x >= 0.00001 I get useful numeric results, e.g.

resp=0.00025871503616237216

for x =0.00001. However, for 0< x < 0.00001 this method fails. With a small argument x and

var('x,y,mx')
x=0.000000001
resp=mathematica.set(mx,x)
mathematica('MeijerG[{{1, 3/2}, {}}, {{1, 1}, {1/2}}, mx]'),

With this small argument, I obtain:

resp=MeijerG[{{1, 3/2}, {}}, {{1, 1}, {1/2}}, -9. + 1.*e]

Obviously, this behavious is caused by the python interpreter: It converts pure decimal presentation of numbers (see previous example) into their scientific presentation. And, as I have learned from contributions in the Mathematica's stack exchange, Mathematica doesn't accept formatted numbers like ScientficForm, etc, for numerical evaluation of functions. Thus, Mathematica lets requested numeric evaluation undone. I haven't found any hints how to prevent python from expressing the argument in scientific format. Is it possible by any means to circumvent this problem?

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[ Comment converted to answer... ]

Emmanuel Charpentier gravatar imageEmmanuel Charpentier ( 2019-11-27 14:00:34 -0600 )edit

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answered 2019-11-28 08:17:08 -0600

Emmanuel Charpentier gravatar image

updated 2019-11-28 08:19:48 -0600

Converting my previous comment to an answer.

This is IMNSHO a bug, reported as Trac#28814.

The conversion is incorrect in the Sage --> Mathematica direction:

sage: 0.000001._mathematica_()
-7 + 10.*e

But doesn't affect rationals:

sage: QQ(0.000001)._mathematica_()
1/1000000

A workaround is to cast those inconvenient floating point quantities to rational approximations:

sage: mathematica.N(mathematica.Sin(0.000001)).sage()
-1.0*sin(-10.0*e + 7.0)
sage: mathematica.N(mathematica.Sin(QQ(0.000001))).sage()
9.999999999998333e-07

[ Note : In general, avoiding floats in the solution of mathematical problems is IMNSHO good heuristics, if not necessarily good numerical analysis... ]

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Asked: 2019-11-27 09:30:46 -0600

Seen: 59 times

Last updated: Nov 28