PHYS 252

Getting Started With Gnuplot

Gnuplot is a simple program for displaying and printing graphs.
To get started:

1. Read Getting Started With Visual C++, in Supplementary Info for Lecture 1.
2. Make a new project in Visual C++, e.g. with project name mar27b.
3. Create source file: enter the following example as main.c

   /* Output square and cube */
   #include   <stdio.h>   
   main()                  
   {                               
   	FILE *fp = fopen("out.dat","w") ;  /* opens file "out.dat", with label fp. */
   	                                   /* The "w" means we are going to write to the file */
   	double x  ;     
   	x = -5. ;
   	while (x<5.) {      		   /* loop over x-coordinate as long as x<5 */
   	    fprintf(fp,"%lf %lf %lf\n",x,x*x,x*x*x);    /* output to file square and cube */
   	    x = x + .1;      	  	   /* increase x for next step in loop */
   	}
           fclose(fp) ;       		   /* close file */
   }
   

4. Create data file "out.dat":
• Compile and run main.c (ctrl-F5). This should create the file out.dat.
• To see out.dat, in Visual C++ click on Project->Show all Files. Then right click on "out.dat" in left-hand panel -> Open With "Notepad"
5. Plot "out.dat" with gnuplot:
• To open gnuplot, double-click on Desktop->"Shortcut to wgnuplot"
• In gnuplot, click File->Change Directory, and find directory with "out.dat". In this case, it's at Desktop->[your name]->mar27b->mar27b
• Type: plot "out.dat". Plot should come up.
6. Some other useful gnuplot commands:
• To plot column 1 vs. 3: "plot [filename] using 1:3"
• To plot column 2 vs. 3: "plot [filename] using 2:3"
• "plot [filename] with lines"
• Try: "plot [filename] using 1:2 with lines, [filename] using 1:3 with points"
• "set xrange [-25:25]". then "set yrange [-10:10]". then "replot".
• "reset"
• To print, right-click upper left corner of plot
• Try "help" or "help plot"

See also this website or this website for more gnuplot tips