Status: New Owner: ---- Labels: Type-Defect Priority-Medium
New issue 1857 by renierm: evalf/simplify accuracy http://code.google.com/p/sympy/issues/detail?id=1857 Sympy seems to lose accuracy with simplification and evalf use. As expressions are simlified accuracy seems to be lost. Consider the following defined constants. import sympy mu0 = 4*sympy.pi*1e-7 c0 = sympy.Real(299792458) eps0 = 1/(c0**2*mu0) # As one would expect print 4e-7*sympy.pi.evalf(100) - mu0.evalf(100) # returns x.xxE-108 which is equivalent to 0 (=0) # but print 1/(c0**2*mu0.evalf(100)) - eps0.evalf(100) # returns x.xxE-28 (!= 0) # and print sympy.sqrt(eps0).evalf(100) - sympy.sqrt(eps0.evalf(100)) # returns x.xxE-22 (!= 0) # while print (sympy.Real(1.0e9)*sympy.sqrt(eps0)).evalf(100) - sympy.Real(1.0e9)*sympy.sqrt(eps0.evalf(100)) # returns x.xxE-13 (!= 0) It seems that as sympy internally simplifies expressions, some assumption in precision is being made, e.g., pi is evaluated at some stage to some precision and then this rounding error is propagated. Renier -- You received this message because you are listed in the owner or CC fields of this issue, or because you starred this issue. You may adjust your issue notification preferences at: http://code.google.com/hosting/settings -- You received this message because you are subscribed to the Google Groups "sympy-issues" group. To post to this group, send email to sympy-iss...@googlegroups.com. To unsubscribe from this group, send email to sympy-issues+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy-issues?hl=en.
