Catalogue of GP/PARI Functions: Plotting functions
Author: Karim Belabas
Keywords: PARI, GP, DOC

## Plotting functions

Although plotting is not even a side purpose of PARI, a number of plotting functions are provided. There are three types of graphic 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

(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 attached 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 attached to that window (which can be changed using the `plotcolor` function) 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 `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, use `plotkill`. It is not possible to partially erase a window: erase it completely, initialize it again, 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 `plotscale`. 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.

Plotting functions are platform independent, but a number of graphical drivers are available for screen output: X11-windows (including Openwindows and Motif), Windows's Graphical Device Interface, the Qt and FLTK graphical libraries and one may even write the graphical objects to a PostScript or SVG file and use an external viewer to open it. 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. This window can be closed, enlarged or reduced using the standard window manager functions. No zooming procedure is implemented though.

#### Functions for PostScript or SVG output

in the same way that `printtex` allows you to have a TeX output corresponding to printed results, the functions `plotexport`, `plothexport` and `plothrawexport` convert a plot to a character string in either `PostScript` or `Scalable Vector Graphics` format. This string can then be written to a file in the customary way, using `write`. These export routines are available even if no Graphic Library is.

#### parploth(X = a, b, expr, {flags = 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. `parploth` may evaluate `expr` thousands of times; given the relatively low resolution of plotting devices, few significant digits of the result will be meaningful. Hence you should keep the current precision to a minimum (e.g. 9) before calling this function.

n specifies the number of reference point on the graph, where a value of 0 means we use the hardwired default values (1000 for general plot, 1500 for parametric plot, and 8 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 [f1(X),...,fk(X)], and then all the curves y = fi(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:

      parploth(X=0,2*Pi,[sin(X),cos(X)], "Parametric")
      parploth(X=0,2*Pi,[sin(X),cos(X)])
      parploth(X=0,2*Pi,[X,X,sin(X),cos(X)], "Parametric")

draw successively a circle, two entwined sinusoidal curves and a circle cut by 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

      parploth(X=-1,1, sin(1/X), "Recursive")
      parploth(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

      parploth(x = -20, 20, sin(x), "Recursive")

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 used in conjunction with `plotscale` when graphing multiple functions on a rectwindow (as a `plotrecth` call):

        s = plothsizes();
        plotinit(0, s[2]-1, s[2]-1);
        plotscale(0, -1,1, -1,1);
        plotrecth(0, t=0,2*Pi, [cos(t),sin(t)], "Parametric|no_Rescale")
        plotdraw([0, -1,1]);

This way we get a proper circle instead of the distorted ellipse produced by

        parploth(t=0,2*Pi, [cos(t),sin(t)], "Parametric")

* 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.

* 4096 = `Complex`: is a parametric plot but where each member of `expr` is considered a complex number encoding the two coordinates of a point. For instance:

      parploth(X=0,2*Pi,exp(I*X), "Complex")
      parploth(X=0,2*Pi,[(1+I)*X,exp(I*X)], "Complex")

will draw respectively a circle and a circle cut by the line y = x.

The library syntax is `parploth(GEN a,GEN b,GEN code, long flag, long n, long prec)`.

#### 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 minimum (resp. the maximum) of the computed values of the expression is used instead.

#### plotbox(w, x2, y2, {filled = 0})

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. If filled = 1, fill the box.

The library syntax is `void plotbox(long w, GEN x2, GEN y2, long filled)`.

#### plotclip(w)

`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 committing the part you're interested in to the final picture.

The library syntax is `void plotclip(long w)`.

#### plotcolor(w, c)

Set default color to c in rectwindow w. Return [R,G,B] value attached to color. Possible values for c are

* a `t_VEC` or `t_VECSMALL` [R,G,B] giving the color RGB value (all 3 values are between 0 and 255), e.g. `[250,235,215]` or equivalently `[0xfa, 0xeb, 0xd7]` for `antiquewhite`;

* a `t_STR` giving a valid colour name (see the `rgb.txt` file in X11 distributions), e.g. `"antiquewhite"` or an RGV value given by a `#` followed by 6 hexadecimal digits, e.g. `"#faebd7"` for `antiquewhite`;

* a `t_INT`, an index in the `graphcolormap` default, factory setting are

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

but this can be extended if needed.

      ? plotinit(0,100,100);
      ? plotcolor(0, "turquoise")
      %2 = [64, 224, 208]
      ? plotbox(0, 50,50,1);
      ? plotmove(0, 50,50);
      ? plotcolor(0, 2) \\ blue
      %4 = [0, 0, 255]
      ? plotbox(0, 50,50,1);
      ? plotdraw(0);

The library syntax is `GEN plotcolor(long w, GEN c)`.

#### plotcopy(sourcew, destw, dx, dy, {flag = 0})

Copy the contents of rectwindow sourcew to rectwindow destw with offset (dx,dy). If flag's bit 1 is set, dx and dy express fractions of the size of the current output device, otherwise dx and dy are in pixels. dx and dy are relative positions of northwest corners if other bits of flag vanish, otherwise of: 2: southwest, 4: southeast, 6: northeast corners

The library syntax is `void plotcopy(long sourcew, long destw, GEN dx, GEN dy, long flag)`.

#### plotcursor(w)

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

The library syntax is `GEN plotcursor(long w)`.

#### plotdraw(w, {flag = 0})

Physically draw the rectwindow w. More generally, w can be of the form [w1,x1,y1,w2,x2,y2,...] (number of components must be divisible by 3; 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 window on your screen. If flag != 0, x1, y1 etc. express fractions of the size of the current output device

The library syntax is `void plotdraw(GEN w, long flag)`.

#### plotexport(fmt, list, {flag = 0})

Draw list of rectwindows as in `plotdraw(list,flag)`, returning the resulting picture as a character string which can then be written to a file. The format `fmt` is either `"ps"` (PostScript output) or `"svg"` (Scalable Vector Graphics).

       ? plotinit(0, 100, 100);
       ? plotbox(0, 50, 50);
       ? plotcolor(0, 2);
       ? plotbox(0, 30, 30);
       ? plotdraw(0); \\ watch result on screen
       ? s = plotexport("svg, 0);
       ? write("graph.svg", s); \\ dump result to file

The library syntax is `GEN plotexport(GEN fmt, GEN list, long flag)`.

#### ploth(X = a, b, expr, {flags = 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. `ploth` may evaluate `expr` thousands of times; given the relatively low resolution of plotting devices, few significant digits of the result will be meaningful. Hence you should keep the current precision to a minimum (e.g. 9) before calling this function.

n specifies the number of reference point on the graph, where a value of 0 means we use the hardwired default values (1000 for general plot, 1500 for parametric plot, and 8 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 [f1(X),...,fk(X)], and then all the curves y = fi(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)], "Parametric")
      ploth(X=0,2*Pi,[sin(X),cos(X)])
      ploth(X=0,2*Pi,[X,X,sin(X),cos(X)], "Parametric")

draw successively a circle, two entwined sinusoidal curves and a circle cut by 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), "Recursive")
      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), "Recursive")

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 used in conjunction with `plotscale` when graphing multiple functions on a rectwindow (as a `plotrecth` call):

        s = plothsizes();
        plotinit(0, s[2]-1, s[2]-1);
        plotscale(0, -1,1, -1,1);
        plotrecth(0, t=0,2*Pi, [cos(t),sin(t)], "Parametric|no_Rescale")
        plotdraw([0, -1,1]);

This way we get a proper circle instead of the distorted ellipse produced by

        ploth(t=0,2*Pi, [cos(t),sin(t)], "Parametric")

* 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.

* 4096 = `Complex`: is a parametric plot but where each member of `expr` is considered a complex number encoding the two coordinates of a point. For instance:

      ploth(X=0,2*Pi,exp(I*X), "Complex")
      ploth(X=0,2*Pi,[(1+I)*X,exp(I*X)], "Complex")

will draw respectively a circle and a circle cut by the line y = x.

The library syntax is `ploth(void *E, GEN (*eval)(void*, GEN), GEN a, GEN b, long flags, long n, long prec)`,

#### plothexport(fmt, X = a, b, expr, {flags = 0}, {n = 0})

Plot of expression expr, X goes from a to b in high resolution, returning the resulting picture as a character string which can then be written to a file.

The format `fmt` is either `"ps"` (PostScript output) or `"svg"` (Scalable Vector Graphics). All other parameters and flags are as in `ploth`.

       ? s = plothexport("svg", x=1,10, x^2+3);
       ? write("graph.svg", s);

The library syntax is `plothexport(GEN fmt, void *E, GEN (*eval)(void*, GEN), GEN a, GEN b, long flags, long n, long prec)`,

#### plothraw(X, Y, {flag = 0})

Given X and Y two vectors of equal length, plots (in high precision) the points whose (x,y)-coordinates are given in X and Y. 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`.

The library syntax is `GEN plothraw(GEN X, GEN Y, long flag)`.

#### plothrawexport(fmt, X, Y, {flag = 0})

Given X and Y two vectors of equal length, plots (in high precision) the points whose (x,y)-coordinates are given in X and Y, returning the resulting picture as a character string which can then be written to a file. The format `fmt` is either `"ps"` (PostScript output) or `"svg"` (Scalable Vector Graphics).

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`.

The library syntax is `GEN plothrawexport(GEN fmt, GEN X, GEN Y, long flag)`.

#### plothsizes({flag = 0})

Return data corresponding to the output window in the form of a 8-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, width and height of display, if applicable. If display has no sense, e.g. for svg plots or postscript plots, then width and height of display are set to 0.

If flag = 0, sizes of ticks and characters are in pixels, otherwise are fractions of the screen size

The library syntax is `GEN plothsizes(long flag)`.

#### plotinit(w, {x}, {y}, {flag = 0})

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; omitting either x or y means we use the full size of the device in that direction. 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);

The library syntax is `void plotinit(long w, GEN x = NULL, GEN y = NULL, long flag)`.

#### plotkill(w)

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.

The library syntax is `void plotkill(long w)`.

#### 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.

The library syntax is `void plotlines(long w, GEN X, GEN Y, long flag)`.

#### plotlinetype(w, type)

This function is obsolete and currently a no-op.

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.

The library syntax is `void plotlinetype(long w, long type)`.

#### plotmove(w, x, y)

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

The library syntax is `void plotmove(long w, GEN x, GEN y)`.

#### plotpoints(w, 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).

If you draw few points in the rectwindow, they will be hard to see; in this case, you can use filled boxes instead. Compare:

      ? plotinit(0, 100,100); plotpoints(0, 50,50);
      ? plotdraw(0)
      ? plotinit(1, 100,100); plotmove(1,48,48); plotrbox(1, 4,4, 1);
      ? plotdraw(1)

The library syntax is `void plotpoints(long w, GEN X, GEN Y)`.

#### plotpointsize(w, size)

This function is obsolete. It is currently a no-op.

Changes the "size" of following points in rectwindow w. If w = -1, change it in all rectwindows.

The library syntax is `void plotpointsize(long w, GEN size)`.

#### plotpointtype(w, type)

This function is obsolete and currently a no-op.

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.

The library syntax is `void plotpointtype(long w, long type)`.

#### plotrbox(w, dx, dy, {filled})

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. If filled = 1, fill the box.

The library syntax is `void plotrbox(long w, GEN dx, GEN dy, long filled)`.

#### 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). Returns a vector for the bounding box.

#### plotrecthraw(w, data, {flags = 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.

The library syntax is `GEN plotrecthraw(long w, GEN data, long flags)`.

#### plotrline(w, dx, dy)

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).

The library syntax is `void plotrline(long w, GEN dx, GEN dy)`.

#### plotrmove(w, dx, dy)

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

The library syntax is `void plotrmove(long w, GEN dx, GEN dy)`.

#### plotrpoint(w, dx, dy)

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).

If you draw few points in the rectwindow, they will be hard to see; in this case, you can use filled boxes instead. Compare:

      ? plotinit(0, 100,100); plotrpoint(0, 50,50); plotrpoint(0, 10,10);
      ? plotdraw(0)

      ? thickpoint(w,x,y)= plotmove(w,x-2,y-2); plotrbox(w,4,4,1);
      ? plotinit(1, 100,100); thickpoint(1, 50,50); thickpoint(1, 60,60);
      ? plotdraw(1)

The library syntax is `void plotrpoint(long w, GEN dx, GEN dy)`.

#### plotscale(w, x1, x2, y1, y2)

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.

The library syntax is `void plotscale(long w, GEN x1, GEN x2, GEN y1, GEN y2)`.

#### plotstring(w, x, {flags = 0})

Draw on the rectwindow w the String x (see Section 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).

The library syntax is `void plotstring(long w, const char *x, long flags)`.

#### psdraw(list, {flag = 0})

This function is obsolete, use plotexport and write the result to file.

The library syntax is `void psdraw(GEN list, long flag)`.

#### psploth(X = a, b, expr, {flags = 0}, {n = 0})

This function is obsolete, use plothexport and write the result to file.

The library syntax is `GEN psploth0(GEN X, GEN b, GEN expr, long flags, long n, long prec)`.

#### psplothraw(listx, listy, {flag = 0})

This function is obsolete, use plothrawexport and write the result to file.

The library syntax is `GEN psplothraw(GEN listx, GEN listy, long flag)`.