yes? shade/T="01-JAN-1994":"12-DEC-1994" \
aglt[D=1,L=@AVE]-aglt[D=2,L=@AVE]
does not in general compute the average from 01-JAN-1994 to
12-DEC-1994 of the two variables and subtract them. You
always need to specify the region for each variable separately
in square brackets to get the calculation right, or regrid one dataset
to the time axis of the other before doing the computation
yes? shade aglt[D=1,T="01-JAN-1994":"12-DEC-1994"@AVE]- \
aglt[D=2,T="01-JAN-1994":"12-DEC-1994"@AVE]
or
yes? let algt2 = algt[d=2,gt=algt[d=1]]
yes? shade/T="01-JAN-1994":"12-DEC-1994" \
aglt[D=1,L=@AVE]-aglt2[L=@AVE]
Try this: make up a couple of time series variables on two
different time axes, and use MODE DIAGNOSTIC to see what
Ferret makes of the calculation. Look at the lines that start with
"doing -->" to see that the average for variable a is correct, but
the averaging for variable b does not have the right time range.
Ferret cannot make sense of the command.
yes? def axis/t="1-jan-1990":"31-dec-1990":1/units=days tday
yes? def axis/t="1-jan-1989":"31-dec-1994":7/units=days tweek
yes? let a = sin(t[gt=tday]/10) * t[gt=tday]/100
yes? let b = cos(t[gt=tweek]/20)* (1-t[gt=tweek]/100)
yes? plot a ! Plot the variables to load them into memory
yes? plot b
yes? set mode diag
yes? list/t="1-jan-1990":"31-dec-1990" a[l=@ave] - b[l=@ave]
dealloc dynamic grid (G002)
NORMAL NORMAL NORMAL
TWEEK
getgrid EX#1 C: 5 I:
1 1 J: 1 1
K: 1 1 L: 1
1
*** NOTE: Ambiguous coordinates on T axis: A[L=@AVE] - B[L=@AVE]
allocate dynamic grid (G001)
NORMAL NORMAL NORMAL
TDAY
strip limits reconciliation : EX#1
eval EX#1 C:
5 I: -111 -111 J: -111 -111 K: -111 -111 L:
1 365
strip --> A[T=01-JAN-199000:00:31-DEC-199000:00@AVE,D=0]
found A
M: 3 I: -111 -111 J: -111 -111 K: -111 -111 L:
1 365
doing --> A[T=01-JAN-199000:00:31-DEC-199000:00@AVE,D=0]
strip --> B[T=01-JAN-198900:00:31-DEC-198900:00@AVE,D=0]
found B
M: 4 I: -111 -111 J: -111 -111 K: -111 -111 L:
1 314
doing --> B[T=01-JAN-198900:00:31-DEC-198900:00@AVE,D=0]
VARIABLE : A[L=@AVE] - B[L=@AVE]
TIME : 01-JAN-1990 00:00 to 31-DEC-1990 00:00
-0.1186
Ansley Manke wrote:
Hi Steve,
When you do a calculation over time when there are two different
time axes involved in the expression, Ferret gives this informational
message just to let you know that the two time averages are different.
It's using each variable's time axis and is doing the calculation you
expected. You could make it absolutely clear what you're doing by
specifying the time interval as a qualifier for each variable, in square
brackets. (I use the backslash continuation character here)yes? shade aglt[D=1,T="01-JAN-1994":"12-DEC-1994"@AVE]- \
aglt[D=2,T="01-JAN-1994":"12-DEC-1994"@AVE]See "region" in the Users Guide index; this is the third way to specify
a region and is almost always the best way to be sure you're doing
what you think you're doing. And, this is also the way to do it if you
want to compare averages over two different time intervals:yes? shade aglt[D=1,T="01-Jan-1994":"12-Jun-1994"@AVE]- \
aglt[D=2,T="13-Jun-1994":"12-Dec-1994"@AVE]Ansley Manke
Steve Knox wrote:
> How can I avoid this ambiguity on the time axis when I'm dealing with 2
> datasets?
> I guess it's confused since it dosen't know which T axis to average over.
> In this case the time periods are the same so the ambiguity doesn't
> matter, but if I want
> to specify different time periods in each dataset how can I do this?
>
> yes? use agltHistoric.cdf
> yes? use agltCENT.cdf
> yes? shade/T="01-JAN-1994":"12-DEC-1994" aglt[D=1,L=@AVE]-aglt[D=2,L=@AVE]
>
> *** NOTE: Ambiguous coordinates on T axis: AGLT[D=1,L=@AVE]-AGLT[D=2,L=@AVE]
>
> Thanks for any help on this.
>
> Steve Knox
> NREL
> Colorado State University--
Ansley Manke Pacific Marine Environmental Laboratory Seattle WA
--
Ansley Manke Pacific Marine Environmental Laboratory Seattle
WA