PLOT Z(X,Y)=<function of X,Y> / TYPE=CONTOUR (with DEVICE=PS or DEVICE=G or as GPLOT) draws a contour plot of the given function of two variables as a raster image. The function is written according to the rules of curve plotting (see CURVES?). X and Y may be replaced by any words. The scaling must be indicated by the SCALE, XSCALE, YSCALE, X and Y specifications, for example, as follows: SCALE=0(0.1)1 X=0,1,0.01 Y=0,1,0.01 The last parameter (0.01) in X and Y specifications gives the steplength. The ranges of XSCALE and X (and YSCALE and Y) must coincide. The function is evaluated in the middle of each cell defined by the X and Y specifications and these function values are mapped to various colours or shades of gray. In the color mapping the function values are assumed to be within the interval (0,1). If they are not, the values are treated modulo 1. This feature is very useful when clear contour curves should be obtained. Before the color mapping, the function values f(x,y) can be linearly tranformed to a*f(x,y)+b by giving a specification ZSCALING=a,b . On the screen, various palettes may be used by the PALETTE specifi- cation. It refers to a text file with extension .PAL. For example, VGAGRAY.PAL gives 16 different shades of gray. On PostScript devices, the true amount of gray shades greatly depends on the resolution. The SCREEN=NEG specification reverses the order of the palette colors or gray shades. Default is SCREEN=POS. On PostScript devices, the SCREEN specification has an extended form SCREEN=<POS | NEG>,<raster_width_(samples/inch)>,<raster_angle> . On the small laser printers (300 pixels/inch), the default setting is SCREEN=POS,60,0 . Example 1: Paraboloid ................................................................................ GPLOT Z(X,Y)=X*X+Y*Y / TYPE=CONTOUR SCALE=-1(0.5)1 X=-1,1,0.05 Y=-1,1,0.05 ZSCALING=0.5,0 PALETTE=VGAGRAY ................................................................................Example 2: Influence curves for correlation coefficientCORR DECA,CUR+1/ VARS=Height,Weight Means, std.devs and correlations of DECA N=48 Variable Mean Std.dev. Height 186.9583 5.090493 Weight 85.56250 6.847600 Correlations: Height Weight Height 1.0000 0.8522 Weight 0.8522 1.0000 ................................................................................ r=0.85 mx=186.96 my=85.56 sx=5.09 sy=6.85 n=48 HEADER=[MAGENTA],Influence_curves_for_correlation_coefficientGPLOT z(x,y)=abs(r*(1-w)+u*v)/wu=sqrt(n/(n*n-1))*(x-mx)/sx v=sqrt(n/(n*n-1))*(y-my)/sy w=sqrt((1+u*u)*(1+v*v)) x=150,220,0.25 y=40,130,0.25 TYPE=CONTOUR SCREEN=NEG 1/0.05=20 ZSCALING=20,0 (One band corresponds to 0.05 increase/decrease in corr.) XSCALE=150(10)220 YSCALE=40(10)130 PALETTE=VGAGRAY ................................................................................ A general sucro for making these plots on the next page!Sucro /INFL_R makes influence curves for the correlation coefficient of two variables of any data set as contour plots.The user may indicate a new point in the graph by the mouse and see its effect to the correlation coefficient. See /INFL_R Example: /INFL_R DECA,Height,Weight,0.05 Reference: http://www.survo.fi/papers/corrcurves.pdf P = More information on PLOT

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