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Maxima Manual

7.1 Definitions for Plotting

Variable: IN_NETMATH [FALSE]

If not nil, then plot2d will output a representation of the plot which is suitable for openplot functions.

Function: OPENPLOT_CURVES list rest-options

Takes a list of curves such as

[[x1,y1,x2,y2,...],[u1,v1,u2,v2,...],..] or [[[x1,y1],[x2,y2],...],.. ]

and plots them. This is similar to xgraph_curves, but uses the open plot routines. Addtional symbol arguments may be given such as "{xrange -3 4}" The following plots two curves, using big points, labeling the first one jim and the second one jane.

openplot_curves([["{plotpoints 1} {pointsize 6} {label jim} {text {xaxislabel {joe is nice}}}"] , [1,2,3,4,5,6,7,8], ["{label jane} {color pink } "], [3,1,4,2,5,7]]);

Some other special keywords are xfun, color, plotpoints, linecolors, pointsize, nolines, bargraph, labelposition, xaxislabel, and yaxislabel.

Function: PLOT2D (expr,range,...,options,..)

Function: PLOT2D ([expr1,expr2,..,exprn],xrange,...,options,..)

EXPR is an expression to be plotted on y axis as a function of 1 variable. RANGE is of the form [var,min,max] and expr is assumed to be an expression to be plotted against VAR. In the second form of the function a list of expressions may be given to plot against VAR. Truncation in the y direction will be performed, for the default y range. It may be specified as an option or using SET_PLOT_OPTION.

plot2d(sin(x),[x,-5,5]); plot2d(sec(x),[x,-2,2],[y,-20,20],[nticks,200]);

Function: xgraph_curves(list)

graphs the list of `point sets' given in list by using xgraph.

A point set may be of the form

[x0,y0,x1,y1,x2,y2,...] or [[x0,y0],[x1,y1],....]

A point set may also contain symbols which give labels or other information.

xgraph_curves([pt_set1,pt_set2,pt_set3]);

would graph the three point sets as three curves.

pt_set:append(["NoLines: True","LargePixels: true"], [x0,y0,x1,y1,...])

would make the point set [and subsequent ones], have no lines between points, and to use large pixels. See the man page on xgraph for more options to specify.

pt_set:append([concat("\"","x^2+y")],[x0,y0,x1,y1,...])

would make there be a "label" of "x^2+y" for this particular point set. The " at the beginning is what tells xgraph this is a label.

pt_set:append([concat("TitleText: Sample Data")],[x0,...])

would make the main title of the plot be "Sample Data" instead of "Maxima PLot".

To make a bar graph with bars which are .2 units wide, and to plot two possibly different such bar graphs:

xgraph_curves( [append(["BarGraph: true","NoLines: true","BarWidth: .2"], create_list([i-.2,i^2],i,1,3)), append(["BarGraph: true","NoLines: true","BarWidth: .2"], create_list([i+.2,.7*i^2],i,1,3)) ]);

A temporary file `xgraph-out' is used.

Variable: PLOT_OPTIONS

Members of this list indicate defaults for plotting. They may be altered using SET_PLOT_OPTION

[X, - 3, 3] [Y, - 3, 3]

are the x range and y range respectively.

[TRANSFORM_XY, FALSE] if not false, should be the output of

make_transform([x,y,z], [f1(x,y,z),f2(x,y,z),f3(x,y,z)])

which produces a transformation from 3 space to 3 space, which will be applied to the graph. A built in one is polar_xy which gives the same as

make_transform([r,th,z],[r*cos(th),r*sin(th),z])

[RUN_VIEWER,TRUE] if not false, means run the viewer software - don't just output a data file.

[GRID,30,30] means plot3d should divide the x range into 30 intervals and similarly the y range.

[COLOUR_Z,false] applies to colouring done with plot_format ps.

[PLOT_FORMAT,OPENMATH] is for plot3d and currently OPENMATH, GNUPLOT, PS, and GEOMVIEW are supported.

There are good quality public domain viewers for these formats. They are openmath, izic, gnuplot, ghostview, and geomview.

The Openmath viewer is in the distribution, and is based on tcl/tk. The executable is `maxima/bin/omplotdata'. The viewer lets you zoom in, slide around, and rotate (if 3 dimensional). This format is also the one used by netmath, for making plots with Netmath. (see `http://www.ma.utexas.edu/users/wfs/netmath.html')

geomview is from the Geometry Center at the University of Minnesota, and is available from `http://www.geom.umn.edu/software/download/geomview.html' or by anonymous ftp from `ftp://ftp.geom.umn.edu/pub/software/geomview/'. It is currently not quite as pretty as izic, but provides excellent support for multiple objects and multiple lights.

gnuplot is everywhere as is ghostview. We also provide mgnuplot, a tcl interface for gnuplot, which lets you rotate the plots using the mouse and a scale.

izic is available by ftp from zenon.inria.fr. Contact one of

{fournier,kajler,mourrain}@sophia.inria.fr.

It has beautiful colour gouraud shading, and very fast wireframe. It runs on X windows.

Function: PLOT3D (expr,xrange,yrange,...,options,..)

Function: PLOT3D ([expr1,expr2,expr3],xrange,yrange,...,options,..)

plot3d(2^(-u^2+v^2),[u,-5,5],[v,-7,7]);

would plot z = 2^(-u^2+v^2) with u and v varying in [-5,5] and [-7,7] respectively, and with u on the x axis, and v on the y axis.

An example of the second pattern of arguments is

plot3d([cos(x)*(3+y*cos(x/2)),sin(x)*(3+y*cos(x/2)),y*sin(x/2)], [x,-%pi,%pi],[y,-1,1],['grid,50,15])

which will plot a moebius band, parametrized by the 3 expressions given as the first argument to plot3d. An additional optional argument [grid,50,15] gives the grid number of rectangles in the x direction and y direction.

/* REal part of z ^ 1/3 */ plot3d(r^.33*cos(th/3),[r,0,1],[th,0,6*%pi], ['grid,12,80],['PLOT_FORMAT,ps], ['TRANSFORM_XY,POLAR_TO_XY],['VIEW_DIRECTION,1,1,1.4], ['COLOUR_Z,true])

Here the View_direction indicates the direction from which we take a projection. We actually do this from infinitely far away, but parallel to the line from view_direction to the origin. This is currently only used in 'ps' plot_format, since the other viewers allow interactive rotating of the object.

Another example is a moebius band:

plot3d([cos(x)*(3+y*cos(x/2)), sin(x)*(3+y*cos(x/2)),y*sin(x/2)], [x,-%pi,%pi],[y,-1,1],['grid,50,15]);

or a klein bottle:

plot3d([5*cos(x)*(cos(x/2)*cos(y)+sin(x/2)*sin(2*y)+3.0) - 10.0, -5*sin(x)*(cos(x/2)*cos(y)+sin(x/2)*sin(2*y)+3.0), 5*(-sin(x/2)*cos(y)+cos(x/2)*sin(2*y))], [x,-%pi,%pi],[y,-%pi,%pi],['grid,40,40])

or a torus

plot3d([cos(y)*(10.0+6*cos(x)), sin(y)*(10.0+6*cos(x)), -6*sin(x)], [x,0,2*%pi],[y,0,2*%pi], ['grid,40,40])

We can output to gnplot too:

plot3d(2^(x^2-y^2),[x,-1,1],[y,-2,2],[plot_format,gnuplot])

Sometimes you may need to define a function to plot the expression. All the arguments to plot3d are evaluated before being passed to plot3d, and so trying to make an expression which does just what you want may be difficult, and it is just easier to make a function.

M:MATRIX([1,2,3,4],[1,2,3,2],[1,2,3,4],[1,2,3,3])$ f(x,y):=float(M[?round(x),?round(y)]); plot3d(f,[x,1,4],[y,1,4],['grid,4,4]);

Function: PLOT2D_PS (expr,range)

writes to pstream a sequence of postscript commands which plot EXPR for RANGE. EXPR should be an expression of 1 variable. RANGE should be of the form [variable,min,max] over which to plot expr. see CLOSEPS.

Function: CLOSEPS ()

This should usually becalled at the end of a sequence of plotting commands. It closes the current output stream PSTREAM, and sets it to nil. It also may be called at the start of a plot, to ensure pstream is closed if it was open. All commands which write to pstream, open it if necessary. CLOSEPS is separate from the other plotting commands, since we may want to plot 2 ranges or superimpose several plots, and so must keep the stream open.

Function: SET_PLOT_OPTION (option)

option is of the format of one of the elements of the PLOT_OPTIONS list. Thus

SET_PLOT_OPTION([grid,30,40])

would change the default grid used by plot3d. Note that if the symbol grid has a value, then you should quote it here:

SET_PLOT_OPTION(['grid,30,40])

so that the value will not be substituted.

Function: PSDRAW_CURVE (ptlist)

Draws a curve connecting the points in PTLIST. The latter may be of the form [x0,y0,x1,y1,...] or [[x0,y0],[x1,y1],...] The function JOIN is handy for taking a list of x's and a list of y's and splicing them together. PSDRAW_CURVE simply invokes the more primitive function PSCURVE. Here is the definition:

(defun $psdraw_curve (lis) (p "newpath") ($pscurve lis) (p "stroke"))

?DRAW2D may also be used to produce a list

points1:?draw2d(1/x,[.05,10],.03)

Function: PSCOM (com)

COM will be inserted in the poscript file eg

pscom("4.5 72 mul 5.5 72 mul translate 14 14 scale");