Re: [Visualpython-users] vector precision?

[Jonathan B. <jbr...@ea...>]

On Tue, 2006-04-25 at 19:16 -0700, Martin Mason wrote:
> Hi Folks,
> 
>  
> 
> Just finishing up  a program to convert observations of RA and Dec
> into orbital elements.  I am trying to match the precision of my
> measuring instruments, which means I need to worry about how the
> vector object stores its components.  I know that the regular float
> variable type has 53 bits of precision.  When I display the contents
> of the vector, it seems like it is truncating it to something like 24
> bits.  Is this just in the display or is this real? IE
> 
> Angular Momentum <0.122495, 0.227241, 1.46103>
> Magnitude of Angular Momentum 1.48366502545
> 
>  
> 
> Is the output just hiding the extra digits or are they disappearing?
> Anyone done any testing on this?

visual.vector stores its components as 3 C "double" variables, which are
equivalent to Python floats.  The display is deliberately truncated in
vector.__str__(), but you can provide your own version of that function
that provides the full resolution if you wish.

def my_vector_str(self):
	return "<%.15e, %.15e, %.15e>" %(self.x, self.y, self.z)
visual.vector.__str__ = my_vector_str

HTH,
-Jonathan