# [ncl-talk] Regarding trend_manken function

Ipsita Putatunda ipsita.putatunda at gmail.com
Sun Jan 3 10:47:42 MST 2021

```Thanks a lot Dennis for clarifying my doubts.

But what is the difference between pc(0) and PC? And why we are doing
(1-pc(0)).
As per the function tren_manken documentation pc(0) is giving the
probability to reject the null Hypothesis. Then what is PC actually?

Ipsita

On Sun, Jan 3, 2021, 10:17 PM Dennis Shea <shea at ucar.edu> wrote:

> From Example 1 which compares NCL's *trend_manken*
> <http://www.ncl.ucar.edu/Document/Functions/Built-in/trend_manken.shtml>
> with results an *R* function
>
>      c  = (/-1,2,-3,4,-5,6,-7,8,-9,10,-11,12/)
>      pc = *trend_manken*(c, False, 0)     ; pc(0)=*0.2683*,   pc(1)=1.0
>
> For comparison, on the last example R (after loading the 'Kendall'
> library) returns:
>
>     < *library(Kendall)*
>     > q  <- c(-1,2,-3,4,-5,6,-7,8,-9,10,-11,12)
>     > x  <- c(1,2,3,4,5,6,7,8,9,10,11,12)
>     > qx <-Kendall(x,y)
>     > qx
> R returns
>       tau = 0.0909, *2-sided *pvalue =*0.7317*    (Note: 1-0.7317= *0.2683* which matches NCL)
> ====
>
> So two-sided
> ====
>
> Run the above example in Python.  That should give you a baseline comparison.
> *******************************************************************************
> Another R example:   *https://www.statology.org/mann-kendall-trend-test-r/* <https://www.statology.org/mann-kendall-trend-test-r/>
> *******************************************************************************
>
> prc = (/31.69,29.77,31.70,33.06,31.31,32.72,31.18,29.90,29.17,31.48,28.11,32.61 \
>        ,31.31,30.96,28.40,30.68,33.67,28.65,30.62,30.21,28.79,30.92,30.92,28.13 \
>        ,30.51,27.63,34.80,32.10,33.86,32.33,25.69,30.60,32.85,30.31,27.71,30.34 \
>        ,29.14,33.41,33.51,29.90,32.69,32.34,35.01,33.05,31.15,36.36,29.83,33.70 \
>        ,29.81,32.41,35.90,37.45,30.39,31.15,35.75,31.14,30.06,32.40,28.44,36.38 \
>        ,31.73,31.27,28.51,26.01,31.27,35.57,30.85,33.35,35.82,31.78,34.25,31.43 \
>        ,35.97,33.87,28.94,34.62,31.06,38.84,32.25,35.86,32.93,32.69,34.39,33.97 \
>        ,32.15,40.16,36.32/)
>
>  pc = *trend_manken(*prc, False, 0)
>  print(pc)
>  print("============")
>  *PC = 1-pc(0)*
>  print("PC=1-pc(0)="+PC)
>
> Variable: pc
> Type: float
> Total Size: 8 bytes
>             2 values
> Number of Dimensions: 1
> Dimensions and sizes:	[2]
> Coordinates:
> (0)	0.9997079
> (1)	0.03999999
> (0)	============
> (0)	*PC=1-pc(0)=0.000292063   <=== matches R*
>
>
> On Sat, Jan 2, 2021 at 11:45 PM Ipsita Putatunda via ncl-talk <
> ncl-talk at mailman.ucar.edu> wrote:
>
>> Dear ncl users,
>> I have gone through the function trend_manken, but I have few doubts as
>> follows-
>> The probability we are getting from this function is two-tailed or
>> one-tailed?
>> Using this function I am getting one of my trend probability 0.97 whereas
>> using python I am getting the value 0.022 which is giving a
>> significantly strong trend.
>> Any help in this regard would be highly appreciated.
>>
>> Thanking you,
>> Ipsita
>>
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>
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