gnuplot_snippets

This snippets produces a lattice of plots using a single input matrix.

static void printone(FILE *f, double width, double height, double margin, int xposn, int yposn, const apop_data *d); //see below

/* This produces a Gnuplot file that will produce an array of 2-D
 plots, one for each pair of columns in the data set. Along the diagonal
 is a plot of the variable against itself---a density plot of the variable.

 \param d  The data set whose (matrix) columns will be compared.
 \param f  The output pipe. E.g., fopen("lattice.gnuplot", "w") or popen("gnuplot --persist", "w")
*/
void apop_plot_lattice(const apop_data *d, FILE *f){
    double  width  = 1.2,//feel free to make these variable inputs.
            height = 1.2;
    double  margin = 0;
    fprintf(f, "set size %g, %g\n"
                "set rmargin 5\n"
                "set lmargin -1\n"
                "set tmargin 2.4\n"
                "set bmargin -2\n"
                "set origin %g, %g       \n"
                "set multiplot   #layout %zu, %zu downwards        \n"
                "unset xtics; unset xlabel; unset ytics; unset ylabel\n"
                "set nokey           \n"
        , width, height, margin,margin, d->matrix->size2, d->matrix->size2);
    for (size_t i = 0; i< d->matrix->size2; i++)
        for (size_t j = 0; j< d->matrix->size2; j++)
            printone(f, width, height, margin, i, j, d);
    fprintf(f, "unset multiplot\n");
}

/* the next function plots a single graph for the \ref apop_plot_lattice  fn */
static void printone(FILE *f, double width, double height, double margin, int xposn, int yposn, const apop_data *d){
    //pull two columns
    size_t count    = d->matrix->size2;
    double nudge    = 0.08;
    gsl_vector  v1  = gsl_matrix_column(d->matrix, xposn).vector;
    gsl_vector  v2  = gsl_matrix_column(d->matrix, yposn).vector;
    gsl_matrix  *m  = gsl_matrix_alloc(d->matrix->size1, 2);
    gsl_matrix_set_col(m, 0, &v1);
    gsl_matrix_set_col(m, 1, &v2);
    double sizex    = (double)(width - margin * (count -1))/count;
    double sizey    = (double)(height - margin * (count -1))/count;
    double offx     = width - (sizex +margin-nudge)* (count - xposn) - nudge*count;
    double offy     = height - (sizey +margin-nudge)* (1 + yposn) - nudge*count;
        fprintf(f, "unset y2tics; unset y2label; unset ytics; unset ylabel\n");
        fprintf(f, "unset x2tics; unset x2label; unset xtics; unset xlabel\n");
    fprintf(f, "set size   %g, %g\n"
               "set origin %g, %g\n"
                ,  sizex, sizey, offx, offy);
    //Gnuplot has no way to just set a label with no plot, so 
    //labels have to be drawn with a long offset from one of the
    //plots we do display.
    if (xposn  == yposn+1)
        fprintf(f, "set label %i '%s' center at graph %g, %g\n",yposn+1, (d->names->colct >yposn)? d->names->col[yposn]: "",  -0.5, 0.5);
    if ((yposn == count-1) && (xposn  == count-2))
        fprintf(f, "set label %zu '%s' center at graph %g, %g\n",count, (d->names->colct >count -1)? d->names->col[count -1]: "",  1.5, 0.5);
    if (xposn != yposn){
        fprintf(f, "plot '-'\n");
        fflush(f);
        apop_matrix_print(m, NULL, f, 'p');
        fprintf(f,"e\n");
        gsl_matrix_free(m);
    }
    if (xposn  == yposn+1)
        fprintf(f, "unset label %i \n",yposn+1);
    if ((yposn == count-1) && (xposn  == count-2))
        fprintf(f, "unset label %zu\n",count);
}

Here is a triangle plot, where points are placed based on the relative weight of three variables.

/** This produces a nifty triangle plot from an input matrix with three
 columns. Each row is plotted inside an equilateral triangle such that
 (1, 0, 0) is the lower left corner, (0, 1, 0) the lower right corner,
 and (0, 0, 1) the middle, upper corner. 

\image html "triangle.png" "A triangle plot with a smattering of data points."

\li Gnuplot will rescale for you, so you don't need to worry about whether the row sums to one. 
\li See \ref apop_prep_output for more on how printing settings are set.
\li See also the legible output section of the \ref outline for more details and examples.
\li This function uses the \ref designated syntax for inputs.
*/
void apop_plot_triangle(apop_data *in, FILE *f){
    Apop_stopif(!in, return, 0, "You sent me a NULL data set.");
    if (in->names && in->names->colct>=3){
        fprintf(f, "set label '%s' at -0.03, 0 right; \n", in->names->col[0]);
        fprintf(f, "set label '%s' at 1.03, 0 left; \n", in->names->col[1]);
        fprintf(f, "set label '%s' at 0.5, 1/sqrt(2)+0.05 center; \n", in->names->col[2]);
    }
    fprintf(f,
        " set size square;      \n"
        " set noborder; set nogrid;         \n"
        " set noxtics; set noytics;         \n"
        " set nokey;        \n"
        " set lmargin 10;       \n"
        " set bmargin 3;        \n"
        " set tmargin 5;        \n"
        " set arrow 1 from 0,0 to 1,0 nohead        \n"
        " set arrow 2 from 0.5,1/sqrt(2) to 1,0 nohead      \n"
        " set arrow 3 from 0.5,1/sqrt(2) to 0,0 nohead      \n"
        " unset title       \n"
        " set xrange [-.1:1.1]      \n"
        " set yrange [-.1:0.81]     \n"
        " plot '-' using (($2 + $3/2)/($1+$2+$3)):($3/($1+$2+$3)/sqrt(2)) with points;         \n"
    );
    gsl_matrix *triplets = Apop_subm(in->matrix, 0,0, in->matrix->size1,3);
    apop_matrix_print(triplets, .output_pipe=f, .output_type='p');
}