Syntax: CONTOUR\COLOURS colr { x y } v num { min }
CONTOUR\INTERP\COLOURS colr ntrp { x y } v num { min }
CONTOUR\SPECIFIC\COLOURS colr { x y } v lvls
CONTOUR\SPECIFIC\INTERP\COLOURS colr ntrp { x y } v lvls
Colour contours can be obtained using the \COLOUR qualifier. A colour
vector, colr, is expected as the first parameter. The length of colr
should be the same as the number of contours requested.
By default, the vectors x and y are assumed to represent rectangular coordinates. If the \POLAR qualifier is used, x and y are assumed to represent polar coordinates, with x the radial component and y the angular component, in degrees. The values are converted to rectangular coordinates, but the vectors are unchanged.
Syntax: CONTOUR { x y } v nctr { min { incr }}
By default, the number of contours, nctr, must be provided. Exact contour
levels can be requested by using the \SPECIFIC qualifier, or by specifying
the minimum contour level, min, and the contour level increment, incr, or,
by specifying a negative number of contours, nctr<0.
If nctr>0 and the increment is not specified, the actual number of
contours drawn may not be the same as the number that was asked for, since
`nice' contour levels will be selected and the range of values may not be
neatly divisible by the requested number. If the minimum is provided, but
not the increment, a `nice' value close to min will be used instead of the
actual data minimum. If the minimum and the increment are both specified,
those exact values will be used for the contour levels.
Additional Information on:
By default, contours are labeled with the actual contour level, using three significant digits. See \LEGEND for an alternate contour labeling facility.
Additional Information on:
The contour levels are automatically stored in a vector named CCONT. If the \COORDINATES qualifier is used, the x and y coordinates of each contour level are automatically stored in the columns of matrices named XCNT and YCNT. The number of points stored for each level is the first element of each column. For example, XCNT[1,nc] (=n1) is the number of points making up contour number nc, while XCNT[2:n1+1,nc] and YCNT[2:n1+1,nc] would contain the x and y coordinates of the nc_th contour level. Each time the CONTOUR command is entered, these matrices are emptied and replaced, so if you wish to keep them, they should be renamed or copied into other variables.
By default, axes are drawn for the contour plot. If the \NOAXES qualifier is used, the current axis scales will be used and no axes will be drawn. Use this qualifier when overlaying a contour plot on an existing graph.
By default, the contours are labeled with the actual contour level, using three significant digits. If \NOAXES is used, then no legend is allowed. If the \LEGEND qualifier is used, then the contours are labeled with an integer index and the list of indices corresponding to the actual contour levels, the legend, is plotted along the right side of the axes. If areas and/or volumes are requested, using \AREAS and/or \VOLUMES, these values will also appear in the legend. If you want to add more contours, re-issue the same contour command with the \CONTINUE qualifier and the legend will be continued from where it left off. You must have used the \-RESET\CONTINUE qualifiers on the previous CONTOUR command if you intend to use add contours using a succeeding CONTOUR command. The contour value legend entries are written using the LEGFRMT format and with height given by LEGSIZ, both of which are changed with the SET command.
Additional Information on:
If you draw a contour plot with the intention of adding more contours, use the \CONTINUE\-RESET qualifiers. Then the internal settings are saved and reused on succeeding CONTOUR\CONTINUE\-RESET commands. Whenever the graphics is cleared, say with the CLEAR command, the contour settings are reset, so you get a fresh plot. If you used \LEGEND originally, it must be used on succeeding CONTOUR\CONTINUE\-RESET commands, and vice-versa. If \CONTINUE is used with three vectors, instead of a matrix, the required grid interpolation is done the first time only.
Suppose that v is a matrix, and that v has n columns and m rows. The vectors x and y are used for scaling the axes. Linear interpolation is used for contouring the matrix. Each matrix element is assumed to be associated with a coordinate point in the plane. The point (x[j],y[i]) is associated with element [i,j] of the matrix. If x and y are allowed to default, the axes that are drawn will represent the matrix indices.
Additional Information on:
If v is a vector, the vectors x and y must be entered, and x, y and v are assumed to represent a scattered set of points, where the value v[i] is the function value corresponding to the point (x[i],y[i]). Contours are computed by successive solution of quintic polynomial equations. The irregularly distributed data points are organized as triangles and the partial derivatives at each point are estimated from the function values of the neighboring points. Areas and volumes cannot be calculated from scattered data.
Additional Information on: