Re: [ferret_users] inconsistent behaviour trying to use min to find location.

[Russ Fiedler <russell.fiedler@xxxxxxxx>]

Hi Rob,

I wonder if there is some floating point rounding going in the immediate
mode evaluation that you can't see (i.e. down at the level of precision)
and the minimum gets missed. 

try instead

let newvar = var - var[t=@min] ! minima at 0
let xloc = var[t=@loc:0]

Russ


On Mon, 2012-03-19 at 07:49 +1100, rdbriggs wrote:
> Hello,
> 
> In the past I've used the
> 
> let vmax = v[x=@max,y=@max]
> 
> and
> 
> let xloc = v[x=@loc:`vmax`]
> 
> commands to successfully find the location of the minimum. But this time I have a problem, can anyone tell me what I am doing wrong?
> 
> My functions are FUNDHS, FUNDHS50
> 
> ! get min
> LET outDHS = funDHS[T=@MIN]
> LET outDHs50 = funDHs50[T=@MIN]
> 
> ! and time it occurs
> LET TDHS= funDHS[T=@LOC:`outDHS`]
> LET TDHs50 = funDHs50[T=@LOC:`outDHs50`]
> 
> LIST outDHS, outDHS50, TDHs, TDHs50
>               DATA SET: ./rreconHs.dat
>               T: -120.5 to 0.5
>   Column  1: OUTDHS is FUNDHS[T=@MIN]
>   Column  2: OUTDHS50 is FUNDHS50[T=@MIN]
>   Column  3: TDHS is FUNDHS[T=@LOC:0.7081349]
>   Column  4: TDHS50 is FUNDHS50[T=@LOC:27.53873]
>            OUTDHS  OUTDHS5  TDHS  TDHS50
> I / *:     0.7081   27.54 -10.00   ....
> 
> 
> ------>  SoTDHS  worksTDHS50  does not ?
> 
> The output from my two functions are
> 
> yes? list FUNDHS, FUNDHS50
> 
> 15    / 106:     50.    163.
> -14    / 107:     33.    130.
> -13    / 108:     20.    109.
> -12    / 109:     10.    104.
> -11    / 110:      3.     32.
> -10    / 111:      1.     28.<  ------ I want to automatically identify this time
> -9     / 112:      2.     28.
> -8     / 113:      7.     32.
> -7     / 114:     16.     41.
> -6     / 115:     28.     52.
> -5     / 116:     44.     68.
> -4     / 117:     64.     87.
> -3     / 118:     88.    110.
> -2     / 119:    115.    137.
> -1     / 120:    145.    167.
> 0      / 121:    180.    201.
> yes? list FUNDHS, FUNDHS50
> 
> 
> improving the precision
> yes? list/form=(2(F9.4)) FUNDHS, FUNDHS50
> 
>   33.1926 130.2298
>    19.8315 108.5893
>    10.4672 104.3460
>     2.9604  32.1601
>     0.7081  27.5387<------ these are the mins
>     2.1548  28.4311
>     7.2379  32.3409
>    15.9903  40.5858
>    28.3927  52.3871
>    44.4533  68.0784
>    64.1537  86.9202
>    87.5170 109.8389
>   114.5442 136.8729
>   145.2063 166.8670
>   179.5263 200.7330
> 
> 
> yes? list FUNDHS50[T=@LOC:27.53873]
>               VARIABLE : T of 27.54 in ((HS_ADJDHS50 - HSOBS)/SIGHS50)^2 + ((TAX-TOBS) / TOBS_SIG)^2
>               FILENAME : rreconHs.dat
>               T        : -120.5 to 0.5 (location of 27.54)
>          ....
> yes? list FUNDHS50[T=@LOC:28]
>               VARIABLE : T of 28 in ((HS_ADJDHS50 - HSOBS)/SIGHS50)^2 + ((TAX-TOBS) / TOBS_SIG)^2
>               FILENAME : rreconHs.dat
>               T        : -120.5 to 0.5 (location of 28)
>           -10.10
> 
> yes? list outDHS50
>               VARIABLE : FUNDHS50[T=@MIN]
>               FILENAME : rreconHs.dat
>               T        : -120.5 to 0.5
>            27.54
> yes? list FUNDHS50[T=@LOC:27.53]
>               VARIABLE : T of 27.53 in ((HS_ADJDHS50 - HSOBS)/SIGHS50)^2 + ((TAX-TOBS) / TOBS_SIG)^2
>               FILENAME : rreconHs.dat
>               T        : -120.5 to 0.5 (location of 27.53)
>          ....
> 
> Any ideas what is going on here ?
> 
> Regards,
> 
> Rob
> 
>