Example 1 - one-dimensional example varying the number of knots (NCL)

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

begin

;----------- Define original data --------------------------------------

xi = (/0.0, 0.1,  0.2,  0.3, 0.5,  0.6, 0.65,  0.8,  0.9, 1./)
yi = (/0.0, 0.8, -0.9, -0.9, 0.9,  1.0, 0.90, -0.8, -0.8, 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 differing number of knots.

knots = 4
yo4 = csa1s(xi,yi,knots,xo)
knots = 7
yo7 = csa1s(xi,yi,knots,xo)
knots = 9
yo9 = csa1s(xi,yi,knots,xo)

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

NCGM=1
X11=0
PS=0

if (NCGM .eq. 1) then
wks = gsn_open_wks("ncgm","nm13n")
end if
if (X11 .eq. 1) then
wks = gsn_open_wks("x11","nm13n")
end if
if (PS .eq. 1) then
wks = gsn_open_wks("ps","nm13n")
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         = -1.2
xyres@tmYLTickEndF           =  1.2
xyres@tmYLTickSpacingF       =  0.6
xyres@tmYRBorderOn           = False     ; Don't draw right axis.
xyres@tmYROn                 = False     ; Don't draw right axis tick marks.

xyres@trXMaxF   =  1.0                   ; Specify data limits.
xyres@trXMinF   =  0.0
xyres@trYMaxF   =  1.2
xyres@trYMinF   = -1.2

xyres@vpHeightF = 0.20                   ; Specify size and location of plot.
xyres@vpWidthF  = 0.80
xyres@vpXF      = 0.13
xyres@vpYF      = 0.88

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

xy = gsn_xy(wks,xo,yo4,xyres)      ; Plot the approximated curve created
; using 4 knots.

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 = 0.03         ; Set the font height.
gsn_text(wks,xy,"knots = 4",0.25,1.0,txres) ; Label the plot.

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             = 0.58      ; Set Y location of plot.
xyres@xyMarkLineMode   = "Lines"   ; Set line mode to "Lines".

xy = gsn_xy(wks,xo,yo7,xyres)      ; Plot the approximated curve
; created using 7 knots.

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

txres@txFontHeightF = 0.03         ; Set font height.
gsn_text(wks,xy,"knots = 7",0.25,1.0,txres) ; Label the plot.

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

;----------- Third graph, same picture --------------------------------

xyres@vpYF             = 0.28      ; Set Y location of plot.
xyres@xyMarkLineMode   = "Lines"   ; Set line mode.

xy = gsn_xy(wks,xo,yo9,xyres)      ; Plot the approximated curve created
; using 9 knots.

xyres@xyMarkLineMode   = "Markers" ; Set line mode.
xy = gsn_xy(wks,xi,yi,xyres)       ; Plot the original points with markers.

txres@txFontHeightF = 0.03         ; Set font height.
gsn_text(wks,xy,"knots = 9",0.25,1.0,txres) ; Label the plot.

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,"Demo for csa1s",.5,.95,txres)

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

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

end
```

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