[ncl-talk] specxy_anal gives maximum frequency less than 0.5
Dennis Shea
shea at ucar.edu
Wed Sep 17 07:18:38 MDT 2014
Oops
N = 100 ; even
df = 1.0/N
frq := df*ispan(1,N/2,1) ; 0 => 0.5
print(frq)
What you are seeing is
N=101 ; odd
df = 1.0/N
frq := df*ispan(1,N/2,1) ; 0 => 0.4950495
This will have to be fixed. A JIRA ticket has been opened
===
N=even .... (N/2) real and imaginary parts 2*(N/2)=N
N=odd .... 2*(N/2) + one real part => N (imaginary part 'undefined')
On Mon, Sep 15, 2014 at 3:09 PM, Maria Gehne - NOAA Affiliate <
maria.gehne at noaa.gov> wrote:
> Hi all,
>
>
> not sure if anyone else has noticed this before. The specxy_anal routine
> returns maximum frequency values that are less that the 0.5 that it should
> return. (The documentation says the last entry of the spectrum is for
> frequency 0.5) This doesn't seem like the desired behavior. Or maybe it is?
>
>
>
> Here is a 4 line script that reproduces the issue:
>
>
> a = fspan(1,100,101)
>
> b = fspan(101,200,101)
>
> dof = specxy_anal(a,b,0,3,0.1)
>
> printMinMax(dof at frq,1)
>
>
> Output:
>
>
> (0)
>
> (0) min=0.00990099 max=0.49505
>
>
>
> Maria
>
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