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Plot coordinate pairs: Difference between revisions
→{{header|C}}: EPS writer
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No one would use the previous code to produce a plot (that looks [http://i40.tinypic.com/f2t0l0.png this way]; instead, normally we produce data through a program, then we plot the data using e.g. [[Plot x, y arrays#gnuplot|gnuplot]] or other powerful tools; the result (with gnuplot and without enhancement) could look [http://i41.tinypic.com/2qivbsn.png like this] instead.
===Writing EPS===
[[File:plot-2d-c.png|center]]Following code creates a plot in EPS format, with auto scaling and line/symbol/color controls. Plotting function loosely follows Matlab command style. Not thorough by any means, just to give an idea on how this kind of things can be coded.
<lang C>#include <stdio.h>
#include <math.h>
#include <string.h>
#define N 40
double x[N], y[N];
void minmax(double x[], int len, double *base, double *step, int *nstep)
{
int i;
double diff, minv, maxv;
*step = 1;
minv = maxv = x[0];
for (i = 1; i < len; i++) {
if (minv > x[i]) minv = x[i];
if (maxv < x[i]) maxv = x[i];
}
if (minv == maxv) {
minv = floor(minv);
maxv = ceil(maxv);
if (minv == maxv) {
minv--;
maxv++;
}
} else {
diff = maxv - minv;
while (*step < diff) *step *= 10;
while (*step > diff) *step /= 10;
if (*step > diff / 2) *step /= 5;
else if (*step > diff / 5) *step /= 2;
}
*base = floor(minv / *step) * *step;
*nstep = ceil(maxv / *step) - floor(minv / *step);
}
/* writes an eps with 400 x 300 dimention, using 12 pt font */
#define CHARH 12
#define CHARW 6
#define DIMX 398
#define DIMY (300 - CHARH)
#define BOTY 20.
int plot(double x[], double y[], int len, char *spec)
{
int nx, ny, i;
double sx, sy, x0, y0;
char buf[100];
int dx, dy, lx, ly;
double ofs_x, ofs_y, grid_x;
minmax(x, len, &x0, &sx, &nx);
minmax(y, len, &y0, &sy, &ny);
dx = -log10(sx);
dy = -log10(sy);
ly = 0;
for (i = 0; i <= ny; i++) {
sprintf(buf, "%g\n", y0 + i * sy);
if (strlen(buf) > ly) ly = strlen(buf);
}
ofs_x = ly * CHARW;
printf("%%!PS-Adobe-3.0\n%%%%BoundingBox: 0 0 400 300\n"
"/TimesRoman findfont %d scalefont setfont\n"
"/rl{rlineto}def /l{lineto}def /s{setrgbcolor}def "
"/rm{rmoveto}def /m{moveto}def /st{stroke}def\n",
CHARH);
for (i = 0; i <= ny; i++) {
ofs_y = BOTY + (DIMY - BOTY) / ny * i;
printf("0 %g m (%*.*f) show\n",
ofs_y - 4, ly, dy, y0 + i * sy);
if (i) printf("%g %g m 7 0 rl st\n",
ofs_x, ofs_y);
}
printf("%g %g m %g %g l st\n", ofs_x, BOTY, ofs_x, ofs_y);
for (i = 0; i <= nx; i++) {
sprintf(buf, "%g", x0 + i * sx);
lx = strlen(buf);
grid_x = ofs_x + (DIMX - ofs_x) / nx * i;
printf("%g %g m (%s) show\n", grid_x - CHARW * lx / 2,
BOTY - 12, buf);
if (i) printf("%g %g m 0 7 rl st\n", grid_x, BOTY);
}
printf("%g %g m %g %g l st\n", ofs_x, BOTY, grid_x, BOTY);
if (strchr(spec, 'r')) printf("1 0 0 s\n");
else if (strchr(spec, 'b')) printf("0 0 1 s\n");
else if (strchr(spec, 'g')) printf("0 1 0 s\n");
else if (strchr(spec, 'm')) printf("1 0 1 s\n");
if (strchr(spec, 'o'))
printf("/o { m 0 3 rm 3 -3 rl -3 -3 rl -3 3 rl closepath st} def "
".5 setlinewidth\n");
if (strchr(spec, '-')) {
for (i = 0; i < len; i++) {
printf("%g %g %s ",
(x[i] - x0) / (sx * nx) * (DIMX - ofs_x) + ofs_x,
(y[i] - y0) / (sy * ny) * (DIMY - BOTY) + BOTY,
i ? "l" : "m");
}
printf("st\n");
}
if (strchr(spec, 'o'))
for (i = 0; i < len; i++) {
printf("%g %g o ",
(x[i] - x0) / (sx * nx) * (DIMX - ofs_x) + ofs_x,
(y[i] - y0) / (sy * ny) * (DIMY - BOTY) + BOTY);
}
printf("showpage\n%%EOF");
return 0;
}
int main()
{
int i;
for (i = 0; i < N; i++) {
x[i] = (double)i / N * 3.14159 * 6;
y[i] = -1337 + (exp(x[i] / 10) + cos(x[i])) / 100;
}
/* string parts: any of "rgbm": color; "-": draw line; "o": draw symbol */
plot(x, y, N, "r-o");
return 0;
}</lang>
=={{header|gnuplot}}==
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