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Plotting functions

And library mode ?   Functions for PostScript output:   High-level plotting functions   Low-level plotting functions   plot   plotbox   plotclip   plotcolor   plotcopy   plotcursor   plotdraw   ploth   plothraw   plothsizes   plotinit   plotkill   plotlines   plotlinetype   plotmove   plotpoints   plotpointsize   plotpointtype   plotrbox   plotrecth   plotrecthraw   plotrline   plotrmove   plotrpoint   plotscale   plotstring   psdraw   psploth   psplothraw  
High-level plotting functions  

High-level plotting functions (all the functions starting with ploth)

in which the user has little to do but explain what type of plot he wants, and whose syntax is similar to the one used in the preceding section.

Low-level plotting functions  

Low-level plotting functions (called rectplot functions, sharing the prefix plot)

, where every drawing primitive (point, line, box, etc.) is specified by the user. These low-level functions work as follows. You have at your disposal 16 virtual windows which are filled independently, and can then be physically ORed on a single window at user-defined positions. These windows are numbered from 0 to 15, and must be initialized before being used by the function plotinit, which specifies the height and width of the virtual window (called a rectwindow in the sequel). At all times, a virtual cursor (initialized at [0,0]) is associated to the window, and its current value can be obtained using the function plotcursor.

A number of primitive graphic objects (called rect objects) can then be drawn in these windows, using a default color associated to that window (which can be changed under X11, using the plotcolor function, black otherwise) and only the part of the object which is inside the window will be drawn, with the exception of polygons and strings which are drawn entirely. The ones sharing the prefix plotr draw relatively to the current position of the virtual cursor, the others use absolute coordinates. Those having the prefix plotrecth put in the rectwindow a large batch of rect objects corresponding to the output of the related ploth function.

Finally, the actual physical drawing is done using the function plotdraw. The rectwindows are preserved so that further drawings using the same windows at different positions or different windows can be done without extra work. To erase a window (and free the corresponding memory), use the function plotkill. It is not possible to partially erase a window. Erase it completely, initialize it again and then fill it with the graphic objects that you want to keep.

In addition to initializing the window, you may use a scaled window to avoid unnecessary conversions. For this, use the function plotscale below. As long as this function is not called, the scaling is simply the number of pixels, the origin being at the upper left and the y-coordinates going downwards.

Note that in the present version 2.3.1 all plotting functions (both low and high level) are written for the X11-window system (hence also for GUI's based on X11 such as Openwindows and Motif) only, though little code remains which is actually platform-dependent. It is also possible to compile gp with either of the Qt or FLTK graphical libraries. A Suntools/Sunview, Macintosh, and an Atari/Gem port were provided for previous versions, but are now obsolete.

Under X11, the physical window (opened by plotdraw or any of the ploth* functions) is completely separated from gp (technically, a fork is done, and the non-graphical memory is immediately freed in the child process), which means you can go on working in the current gp session, without having to kill the window first. Under X11, this window can be closed, enlarged or reduced using the standard window manager functions. No zooming procedure is implemented though (yet).

Functions for PostScript output  

in the same way that printtex allows you to have a TeX output corresponding to printed results, the functions starting with ps allow you to have PostScript output of the plots. This will not be absolutely identical with the screen output, but will be sufficiently close. Note that you can use PostScript output even if you do not have the plotting routines enabled. The PostScript output is written in a file whose name is derived from the psfile default ( ./ if you did not tamper with it). Each time a new PostScript output is asked for, the PostScript output is appended to that file. Hence you probably want to remove this file, or change the value of psfile, in between plots. On the other hand, in this manner, as many plots as desired can be kept in a single file.

And library mode ?  

None of the graphic functions are available within the PARI library, you must be under gp to use them. The reason for that is that you really should not use PARI for heavy-duty graphical work, there are better specialized alternatives around. This whole set of routines was only meant as a convenient, but simple-minded, visual aid. If you really insist on using these in your program (we warned you), the source ( plot*.c) should be readable enough for you to achieve something.

plot(X = a,b,expr,{Ymin},{Ymax})  

crude ASCII plot of the function represented by expression expr from a to b, with Y ranging from Ymin to Ymax. If Ymin (resp. Ymax) is not given, the minima (resp. the maxima) of the computed values of the expression is used instead.


let (x1,y1) be the current position of the virtual cursor. Draw in the rectwindow w the outline of the rectangle which is such that the points (x1,y1) and (x2,y2) are opposite corners. Only the part of the rectangle which is in w is drawn. The virtual cursor does not move.


`clips' the content of rectwindow w, i.e remove all parts of the drawing that would not be visible on the screen. Together with plotcopy this function enables you to draw on a scratchpad before commiting the part you're interested in to the final picture.


set default color to c in rectwindow w. In present version 2.3.1, this is only implemented for the X11 window system, and you only have the following palette to choose from:

1 = black, 2 = blue, 3 = sienna, 4 = red, 5 = green, 6 = grey, 7 = gainsborough.

Note that it should be fairly easy for you to hardwire some more colors by tweaking the files rect.h and plotX.c. User-defined colormaps would be nice, and may be available in future versions.


copy the contents of rectwindow w1 to rectwindow w2, with offset (dx,dy).


give as a 2-component vector the current (scaled) position of the virtual cursor corresponding to the rectwindow w.


physically draw the rectwindows given in list which must be a vector whose number of components is divisible by 3. If list = [w1,x1,y1,w2,x2,y2,...], the windows w1, w2, etc.are physically placed with their upper left corner at physical position (x1,y1), (x2,y2),...respectively, and are then drawn together. Overlapping regions will thus be drawn twice, and the windows are considered transparent. Then display the whole drawing in a special window on your screen.

ploth(X = a,b,expr,{flag = 0},{n = 0})  

high precision plot of the function y = f(x) represented by the expression expr, x going from a to b. This opens a specific window (which is killed whenever you click on it), and returns a four-component vector giving the coordinates of the bounding box in the form [xmin,xmax,ymin,ymax].

Important note: Since this may involve a lot of function calls, it is advised to keep the current precision to a minimum (e.g.9) before calling this function.

n specifies the number of reference point on the graph (0 means use the hardwired default values, that is: 1000 for general plot, 1500 for parametric plot, and 15 for recursive plot).

If no flag is given, expr is either a scalar expression f(X), in which case the plane curve y = f(X) will be drawn, or a vector [f_1(X),...,f_k(X)], and then all the curves y = f_i(X) will be drawn in the same window.

The binary digits of flag mean:

* 1 = Parametric: parametric plot. Here expr must be a vector with an even number of components. Successive pairs are then understood as the parametric coordinates of a plane curve. Each of these are then drawn.

For instance:

ploth(X = 0,2*Pi,[sin(X),cos(X)],1) will draw a circle.

ploth(X = 0,2*Pi,[sin(X),cos(X)]) will draw two entwined sinusoidal curves.

ploth(X = 0,2*Pi,[X,X,sin(X),cos(X)],1) will draw a circle and the line y = x.

* 2 = Recursive: recursive plot. If this flag is set, only one curve can be drawn at a time, i.e.expr must be either a two-component vector (for a single parametric curve, and the parametric flag has to be set), or a scalar function. The idea is to choose pairs of successive reference points, and if their middle point is not too far away from the segment joining them, draw this as a local approximation to the curve. Otherwise, add the middle point to the reference points. This is fast, and usually more precise than usual plot. Compare the results of ploth(X = -1,1,sin(1/X),2) {and} ploth(X = -1,1,sin(1/X)) for instance. But beware that if you are extremely unlucky, or choose too few reference points, you may draw some nice polygon bearing little resemblance to the original curve. For instance you should never plot recursively an odd function in a symmetric interval around 0. Try

  ploth(x = -20, 20, sin(x), 2)

to see why. Hence, it's usually a good idea to try and plot the same curve with slightly different parameters.

The other values toggle various display options:

* 4 = no_Rescale: do not rescale plot according to the computed extrema. This is meant to be used when graphing multiple functions on a rectwindow (as a plotrecth call), in conjunction with plotscale.

* 8 = no_X_axis: do not print the x-axis.

* 16 = no_Y_axis: do not print the y-axis.

* 32 = no_Frame: do not print frame.

* 64 = no_Lines: only plot reference points, do not join them.

* 128 = Points_too: plot both lines and points.

* 256 = Splines: use splines to interpolate the points.

* 512 = no_X_ticks: plot no x-ticks.

* 1024 = no_Y_ticks: plot no y-ticks.

* 2048 = Same_ticks: plot all ticks with the same length.

plothraw(listx,listy,{flag = 0})  

given listx and listy two vectors of equal length, plots (in high precision) the points whose (x,y)-coordinates are given in listx and listy. Automatic positioning and scaling is done, but with the same scaling factor on x and y. If flag is 1, join points, other non-0 flags toggle display options and should be combinations of bits 2^k, k >= 3 as in ploth.


return data corresponding to the output window in the form of a 6-component vector: window width and height, sizes for ticks in horizontal and vertical directions (this is intended for the gnuplot interface and is currently not significant), width and height of characters.


initialize the rectwindow w, destroying any rect objects you may have already drawn in w. The virtual cursor is set to (0,0). The rectwindow size is set to width x and height y. If flag = 0, x and y represent pixel units. Otherwise, x and y are understood as fractions of the size of the current output device (hence must be between 0 and 1) and internally converted to pixels.

The plotting device imposes an upper bound for x and y, for instance the number of pixels for screen output. These bounds are available through the plothsizes function. The following sequence initializes in a portable way (i.e independent of the output device) a window of maximal size, accessed through coordinates in the [0,1000] x [0,1000] range:

s = plothsizes();
 plotinit(0, s[1]-1, s[2]-1);
 plotscale(0, 0,1000, 0,1000);


erase rectwindow w and free the corresponding memory. Note that if you want to use the rectwindow w again, you have to use plotinit first to specify the new size. So it's better in this case to use plotinit directly as this throws away any previous work in the given rectwindow.

plotlines(w,X,Y,{flag = 0})  

draw on the rectwindow w the polygon such that the (x,y)-coordinates of the vertices are in the vectors of equal length X and Y. For simplicity, the whole polygon is drawn, not only the part of the polygon which is inside the rectwindow. If flag is non-zero, close the polygon. In any case, the virtual cursor does not move.

X and Y are allowed to be scalars (in this case, both have to). There, a single segment will be drawn, between the virtual cursor current position and the point (X,Y). And only the part thereof which actually lies within the boundary of w. Then move the virtual cursor to (X,Y), even if it is outside the window. If you want to draw a line from (x1,y1) to (x2,y2) where (x1,y1) is not necessarily the position of the virtual cursor, use plotmove(w,x1,y1) before using this function.


change the type of lines subsequently plotted in rectwindow w. type -2 corresponds to frames, -1 to axes, larger values may correspond to something else. w = -1 changes highlevel plotting. This is only taken into account by the gnuplot interface.


move the virtual cursor of the rectwindow w to position (x,y).


draw on the rectwindow w the points whose (x,y)-coordinates are in the vectors of equal length X and Y and which are inside w. The virtual cursor does not move. This is basically the same function as plothraw, but either with no scaling factor or with a scale chosen using the function plotscale.

As was the case with the plotlines function, X and Y are allowed to be (simultaneously) scalar. In this case, draw the single point (X,Y) on the rectwindow w (if it is actually inside w), and in any case move the virtual cursor to position (x,y).


changes the "size" of following points in rectwindow w. If w = -1, change it in all rectwindows. This only works in the gnuplot interface.


change the type of points subsequently plotted in rectwindow w. type = -1 corresponds to a dot, larger values may correspond to something else. w = -1 changes highlevel plotting. This is only taken into account by the gnuplot interface.


draw in the rectwindow w the outline of the rectangle which is such that the points (x1,y1) and (x1+dx,y1+dy) are opposite corners, where (x1,y1) is the current position of the cursor. Only the part of the rectangle which is in w is drawn. The virtual cursor does not move.

plotrecth(w,X = a,b,expr,{flag = 0},{n = 0})  

writes to rectwindow w the curve output of ploth(w,X = a,b,expr,flag,n).

plotrecthraw(w,data,{flag = 0})  

plot graph(s) for data in rectwindow w. flag has the same significance here as in ploth, though recursive plot is no more significant.

data is a vector of vectors, each corresponding to a list a coordinates. If parametric plot is set, there must be an even number of vectors, each successive pair corresponding to a curve. Otherwise, the first one contains the x coordinates, and the other ones contain the y-coordinates of curves to plot.


draw in the rectwindow w the part of the segment (x1,y1)-(x1+dx,y1+dy) which is inside w, where (x1,y1) is the current position of the virtual cursor, and move the virtual cursor to (x1+dx,y1+dy) (even if it is outside the window).


move the virtual cursor of the rectwindow w to position (x1+dx,y1+dy), where (x1,y1) is the initial position of the cursor ( position (dx,dy) relative to the initial cursor).


draw the point (x1+dx,y1+dy) on the rectwindow w (if it is inside w), where (x1,y1) is the current position of the cursor, and in any case move the virtual cursor to position (x1+dx,y1+dy).


scale the local coordinates of the rectwindow w so that x goes from x1 to x2 and y goes from y1 to y2 (x2 < x1 and y2 < y1 being allowed). Initially, after the initialization of the rectwindow w using the function plotinit, the default scaling is the graphic pixel count, and in particular the y axis is oriented downwards since the origin is at the upper left. The function plotscale allows to change all these defaults and should be used whenever functions are graphed.

plotstring(w,x,{flag = 0})  

draw on the rectwindow w the String x (see Section [Label: se:strings]), at the current position of the cursor.

flag is used for justification: bits 1 and 2 regulate horizontal alignment: left if 0, right if 2, center if 1. Bits 4 and 8 regulate vertical alignment: bottom if 0, top if 8, v-center if 4. Can insert additional small gap between point and string: horizontal if bit 16 is set, vertical if bit 32 is set (see the tutorial for an example).


same as plotdraw, except that the output is a PostScript program appended to the psfile.

psploth(X = a,b,expr)  

same as ploth, except that the output is a PostScript program appended to the psfile.


same as plothraw, except that the output is a PostScript program appended to the psfile.