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Re: How to import data without losing much precision
Posted:
Dec 3, 2012 9:39 PM


On 12/3/2012 4:10 PM, Steven_Lord wrote:
> Symbolic arrays from Symbolic Math Toolbox are generally arbitrary > precision, but make sure you don't limit yourself prior to the construction. > For instance: > > t = 3^(1/3); > x1 = sym(t); > x2 = sym(3)^(1/3); > > x1 and x2 will not be exactly the same as you can see with VPA. In the case > of x1 we took the cube root of 3 in double precision, while in the case of > x2 we converted 3 into a symbolic expression then took the cube root > symbolically. >
Another way to see this is to do
x3 = sym('3^(1/3)')
now x3 and x2 are the same:
 EDU>> vpa(x3) 1.4422495703074083823216383107801 EDU>> vpa(x2) 1.4422495703074083823216383107801 
using '' protects the expression in question from premature evaluation until it gets safe to the symbolic toolbox home
Nasser



