# [Users] reduction in carpet + mismatched declaration in ML_ADMQuantities

heeilkim at gmail.com heeilkim at gmail.com
Fri Jan 7 20:44:55 CST 2011

```Thank all for lots of clarifications,

Erik's second comment answers my question. I thought CarpetReduce only
makes weight values of 0 to 1. But it's actually considering the difference
between each level's volume measure (by volume measure, I mean the cube of
cctk_delta_space), so I don't have to include the measure in the definition
of the integrand. So the Method I actually makes Result II.

Hee Il

> >> 2. Carpet's reduction operators take the relative size of the grid

> >> cells into account. That is, they take into account that finer grid

> >> cells are smaller, and they also take into account that only fractions

> >> of grid cells may contribute near refinement boundaries. (Refinement

> >> boundaries can cut grid cells if you use vertex centered refinement.)

> >> However, Carpet's reduction operators do not take the coordinate

> >> system into account.

> >>

> >> This means that you need to multiply the result with the coarse grid

> >> coordinate volume. (This should probably be changed at some point.)

> >>

> >> -erik

> >>

> >> On Fri, Jan 7, 2011 at 12:00 AM, Hee Il Kim heeilkim at gmail.com> wrote:

> >>> Result I: Mass = (Sum_reflev=0 of capret weighted density(i,j,k) *
> dV_0)

> >>> +

> >>> (Sum_reflev=1 of carpet weighted density(i,j,k) * dV_0) + ...

> >>>

> >>> But what I wanted (expected) to get by defining integrand = density *

> >>> volume_measure" is more accurate one;

> >>>

> >>> Result II: Mass = (Sum_reflev=0 of carpet weighted density(i,j,k) *
> dV_0)

> >>> +

> >>> (Sum_reflev=1 of carpet weighted density(i,j,k) * 1/8 * dV_0) + ...

> >>>

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