# Example 3 - one-dimensional example illustrating extrapolation into data sparse regions (NCL)

```load "\$NCARG_ROOT/lib/ncarg/nclex/gsun/gsn_code.ncl"

begin

;----------- Define original data and initial weighting array -----------

xi = (/0.0, 0.1, 0.2,  0.3,  0.4, 0.5, 0.6, 0.9, 1.0/)
yi = (/0.0, 0.2, 0.4, -0.4, -1.0, 0.2, 0.5, 0.4, 0.0/)

npts   = 101
xo     = fspan(0.0,1.0,npts)  ; Create the output X coordinate array.

xx = (/0.0, 1.0/) ; Create data for a polyline for marking
yy = (/0.0, 0.0/) ; the Y = 0.0 line in each graph.

;--- Calculate approximated function values using different weights.

smth = 0.0
yo1 = csa1xs(xi,yi,-1.,8,smth,0,xo)
smth = 1.0
yo2 = csa1xs(xi,yi,-1.,8,smth,0,xo)

;---- Open workstation, define color map ---------------------------

NCGM=1
X11=0
PS=0

if (NCGM .eq. 1) then
wks = gsn_open_wks("ncgm","nm15n")
end if
if (X11 .eq. 1) then
wks = gsn_open_wks("x11","nm15n")
end if
if (PS .eq. 1) then
wks = gsn_open_wks("ps","nm15n")
end if

cmap = (/                 \
(/1.,1.,1./),   \
(/0.,0.,0./),   \
(/1.,0.,0./),   \
(/0.,0.,1./)    \
/)
gsn_define_colormap(wks,cmap)

;---- Specify resources ---------------------------

txres = True   ; Set up some variables for
xyres = True   ; creating three different
gsres = True   ; resource lists.

xyres@gsnFrame               = False     ; Don't advance the frame.

xyres@tmXTBorderOn           = False     ; Don't draw top axis.
xyres@tmXTOn                 = False     ; Don't draw top axis tick marks.
xyres@tmBorderThicknessF     = 1.0       ; Default thickness is 2.0

xyres@tmXBLabelFont          = 21        ; Change X label font.
xyres@tmXBLabelFontHeightF   = 0.025     ; Change font size.
xyres@tmXBMajorLengthF       = 0.015     ; Default is 0.02.
xyres@tmXBMajorThicknessF    = 1.0       ; Default is 2.
xyres@tmXBMinorLengthF       = 0.0075    ; Default is 0.01.
xyres@tmXBMinorPerMajor      = 4         ; # of minor tick marks per major.
xyres@tmXBMode               = "Manual"  ; Set tick mark mode.
xyres@tmXBTickStartF         = 0.0
xyres@tmXBTickEndF           = 1.0
xyres@tmXBTickSpacingF       = 0.2
xyres@tmXMajorGridThicknessF = 1.0       ; Default is 2.0

xyres@tmYLLabelFont          = 21        ; See explanations for X axes
xyres@tmYLLabelFontHeightF   = 0.025     ; resources.
xyres@tmYLMajorLengthF       = 0.015
xyres@tmYLMajorThicknessF    = 1.0
xyres@tmYLMinorPerMajor      = 0
xyres@tmYLMode               = "Manual"
xyres@tmYLTickStartF         = -2.0
xyres@tmYLTickEndF           =  1.0
xyres@tmYLTickSpacingF       =  1.0
xyres@tmYRBorderOn           = False     ; Don't draw right axis.
xyres@tmYROn                 = False     ; Don't draw right axis tick marks.

xyres@trXMinF   =  0.0
xyres@trXMaxF   =  1.0                   ; Specify data limits.
xyres@trYMinF   = -2.0
xyres@trYMaxF   =  1.0

xyres@vpHeightF = 0.28                   ; Specify size and location of plot.
xyres@vpWidthF  = 0.80
xyres@vpXF      = 0.13
xyres@vpYF      = 0.86

;----------- First graph --------------------------------------------

xy = gsn_xy(wks,xo,yo1,xyres)      ; Plot the approximated curve created
; with equal weights.

xyres@xyMarkLineMode = "Markers"   ; Set line mode to "Markers".
xyres@xyMarkerColor  = 3           ; Set markers to blue.
xyres@xyMarkerSizeF  = 0.025       ; Make markers larger.

xy = gsn_xy(wks,xi,yi,xyres)       ; Mark the original points with blue Xs.

txres@txFont        = 21           ; Change the default font.
txres@txFontHeightF = 0.038        ; Set the font height.
gsn_text(wks,xy,"smth = 0.",0.17,-1.20,txres)

gsres@gsLineColor = 2              ; Set polyline color to red.
gsn_polyline(wks,xy,xx,yy,gsres)   ; Draw polyline at Y=0.

;----------- Second graph, same picture --------------------------------

xyres@vpYF             = 0.43      ; Set Y location of plot.
xyres@xyMarkLineMode   = "Lines"   ; Set line mode to "Lines".

xy = gsn_xy(wks,xo,yo2,xyres)      ; Plot the approximated curve
; created using a weight of 0.5
; to the second input point.

xyres@xyMarkLineMode   = "Markers" ; Set line mode to "Markers".
xy = gsn_xy(wks,xi,yi,xyres)       ; Mark original points.

txres@txFontHeightF = 0.038        ; Set font height.
gsn_text(wks,xy,"smth = 1.",0.17,-1.20,txres)

gsn_polyline(wks,xy,xx,yy,gsres)   ; Draw polyline at Y=0.

;------------- Main title ------------------------------------------

txres@txFontHeightF = 0.04         ; Change the font height.
gsn_text_ndc(wks,":F21:Data sparse areas",.5,.95,txres)

;------------- Plot and clean up  -----------------------------------
frame(wks)

delete(xy)
delete(txres)
delete(gsres)
delete(xyres)

end
```

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