# [ncl-talk] smooth option for xy plots?

Dennis Shea shea at ucar.edu
Tue Feb 21 11:42:16 MST 2017

```To answer an offline query sent to me:
Yes. you did post this question before. However, it was a holiday
yesterday.

---
The EXCEL plot looks nice *but* is it 'correct?' The orange line between
'x' values 4 and 6 is above 4.5. Is that correct? Likely, some
interpolation method was used 'under-the-hood' prior to drawing the curve.
How else can you get the values between (say) x=4 and x=6?

---
http://www.ncl.ucar.edu/Document/Functions/Built-in/ftcurv.shtml
http://www.ncl.ucar.edu/Document/Functions/Built-in/ftsetp.shtml

xi   = (/.../)
yi   = (/.../)
nx  = dimsizes(xi)

N   = 5*nx                ; arbitrary
xo  = fspan(min(x), max(x), N)

;*ftsetp*("sig",0.9)                ; you may have to 'play' with this
; default is 1.0
yo = *ftcurv*(xi, yi, xo)

plot xo,yo

===BETTER===

undef("mimic_excel")
function mimic_excel(xi[*]:numeric, yi[*]:numeric, N[1]:integer,
sig[1]:numeric)
local xo, yo
begin
xo  = fspan(min(xi), max(xi), N)
if (sig.ne.1.0) then
*        ftsetp*("sig",sig)
end if
yo = *ftcurv*(xi, yi, xo)
return( [/ xo, yo/] )   ; return as list variable
end

;==== MAIN

xi   = (/.../)
yi   = (/.../)
nx = dimsizes(xi)
N  = 5*nx               ; 5 is arbitrary
sig = 1.0                ; default

xyo = mimic_excel(xi, yi, N, sig)
xo  = xo[0]
yo  = yo[1]

Good luck

On Mon, Feb 20, 2017 at 1:39 PM, xiaoming Hu <yuanfangcan at hotmail.com>
wrote:

> Hello
>
>
>  I am wondering if NCl provide a smooth option for xy plots like Excel:
>
> In NCL, it seems only straight lines are allowed between data points.
>
>
> Thanks
>
> Xiaoming
>
>
>
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