examples/c/tutor.c

// Tony Richardson
//
// This program is intended to be used as a template for creating simple
// two-dimensional plotting programs which use the PLplot plotting
// library.  The program was written with an emphasis on trying to clearly
// illustrate how to use the PLplot library functions.
//
// This program reads data for M lines with N points each from an input
// data file and plots them on the same graph using different symbols.  It
// draws axes with labels and places a title at the top of the figure.  A
// legend is drawn to the right of the figure.  The input data file must
// have the following format:
//
//    M        N
//    x[1]     y[1][1]     y[1][2]     .     .     .     y[1][M]
//    x[2]     y[2][1]     y[2][2]     .     .     .     y[2][M]
//    x[3]     y[3][1]     y[3][2]     .     .     .     y[3][M]
//     .          .           .        .     .     .        .
//     .          .           .        .     .     .        .
//     .          .           .        .     .     .        .
//    x[N]     y[N][1]     y[N][2]     .     .     .     y[N][M]
//
// (The first line contains the integer values M and N.  The succeeding
// N lines contain the x-coordinate and the corresponding y-coordinates
// of each of the M lines.)
//

#include "plcdemos.h"

static int
error( char *str );

//
// You can select a different set of symbols to use when plotting the
// lines by changing the value of OFFSET.
//

#define OFFSET    2

int
main( int argc, char *argv[] )
{
// ==============  Begin variable definition section. =============

//
// i, j, and k are counting variables used in loops and such. M is the
// number of lines to be plotted and N is the number of sample points
// for each line.
//

    int i, j, k, M, N, leglen;

//
// x is a pointer to an array containing the N x-coordinate values.  y
// points to an array of M pointers each of which points to an array
// containing the N y-coordinate values for that line.
//

    PLFLT *x, **y;

// Define storage for the min and max values of the data.

    PLFLT xmin, xmax, ymin, ymax, xdiff, ydiff;

// Define storage for the filename and define the input file pointer.

    char filename[80], string[80], tmpstr[80];
    FILE *datafile;

// Here are the character strings that appear in the plot legend.

    static char *legend[] =
    {
        "Aardvarks",
        "Gnus",
        "Llamas",
        NULL
    };                          // Make sure last element is NULL

// ==============  Read in data from input file. =============

// Parse and process command line arguments

    (void) plparseopts( &argc, argv, PL_PARSE_FULL );

// First prompt the user for the input data file name

    printf( "Enter input data file name. " );
    scanf( "%s", filename );

// and open the file.

    datafile = fopen( filename, "r" );
    if ( datafile == NULL )     // error opening input file
        error( "Error opening input file." );

// Read in values of M and N

    k = fscanf( datafile, "%d %d", &M, &N );
    if ( k != 2 )               // something's wrong
        error( "Error while reading data file." );

// Allocate memory for all the arrays.

    x = (PLFLT *) malloc( N * sizeof ( PLFLT ) );
    if ( x == NULL )
        error( "Out of memory!" );
    y = (PLFLT **) malloc( M * sizeof ( PLFLT * ) );
    if ( y == NULL )
        error( "Out of memory!" );
    for ( i = 0; i < M; i++ )
    {
        y[i] = (PLFLT *) malloc( N * sizeof ( PLFLT ) );
        if ( y[i] == NULL )
            error( "Out of memory!" );
    }

// Now read in all the data.

    for ( i = 0; i < N; i++ )     // N points
    {
        k = fscanf( datafile, "%f", &x[i] );
        if ( k != 1 )
            error( "Error while reading data file." );
        for ( j = 0; j < M; j++ )         // M lines
        {
            k = fscanf( datafile, "%f", &y[j][i] );
            if ( k != 1 )
                error( "Error while reading data file." );
        }
    }

// ==============  Graph the data. =============

// Set graph to portrait orientation. (Default is landscape.)
// (Portrait is usually desired for inclusion in TeX documents.)

    plsori( 1 );

// Initialize plplot

    plinit();

//
// We must call pladv() to advance to the first (and only) subpage.
// You might want to use plenv() instead of the pladv(), plvpor(),
// plwind() sequence.
//

    pladv( 0 );

//
// Set up the viewport.  This is the window into which the data is
// plotted.  The size of the window can be set with a call to
// plvpor(), which sets the size in terms of normalized subpage
// coordinates.  I want to plot the lines on the upper half of the
// page and I want to leave room to the right of the figure for
// labelling the lines. We must also leave room for the title and
// labels with plvpor().  Normally a call to plvsta() can be used
// instead.
//

    plvpor( 0.15, 0.70, 0.5, 0.9 );

//
// We now need to define the size of the window in user coordinates.
// To do this, we first need to determine the range of the data
// values.
//

    xmin = xmax = x[0];
    ymin = ymax = y[0][0];
    for ( i = 0; i < N; i++ )
    {
        if ( x[i] < xmin )
            xmin = x[i];
        if ( x[i] > xmax )
            xmax = x[i];
        for ( j = 0; j < M; j++ )
        {
            if ( y[j][i] < ymin )
                ymin = y[j][i];
            if ( y[j][i] > ymax )
                ymax = y[j][i];
        }
    }

//
// Now set the size of the window. Leave a small border around the
// data.
//

    xdiff = ( xmax - xmin ) / 20.;
    ydiff = ( ymax - ymin ) / 20.;
    plwind( xmin - xdiff, xmax + xdiff, ymin - ydiff, ymax + ydiff );

//
// Call plbox() to draw the axes (see the PLPLOT manual for
// information about the option strings.)
//

    plbox( "bcnst", 0.0, 0, "bcnstv", 0.0, 0 );

//
// Label the axes and title the graph.  The string "#gm" plots the
// Greek letter mu, all the Greek letters are available, see the
// PLplot manual.
//

    pllab( "Time (weeks)", "Height (#gmparsecs)", "Specimen Growth Rate" );

//
// Plot the data.  plpoin() draws a symbol at each point.  plline()
// connects all the points.
//

    for ( i = 0; i < M; i++ )
    {
        plpoin( N, x, y[i], i + OFFSET );
        plline( N, x, y[i] );
    }

//
// Draw legend to the right of the chart.  Things get a little messy
// here.  You may want to remove this section if you don't want a
// legend drawn.  First find length of longest string.
//

    leglen = 0;
    for ( i = 0; i < M; i++ )
    {
        if ( legend[i] == NULL )
            break;
        j = strlen( legend[i] );
        if ( j > leglen )
            leglen = j;
    }

//
// Now build the string.  The string consists of an element from the
// legend string array, padded with spaces, followed by one of the
// symbols used in plpoin above.
//

    for ( i = 0; i < M; i++ )
    {
        if ( legend[i] == NULL )
            break;
        strcpy( string, legend[i] );
        j = strlen( string );
        if ( j < leglen )         // pad string with spaces
        {
            for ( k = j; k < leglen; k++ )
                string[k] = ' ';
            string[k] = '\0';
        }

        // pad an extra space

        strcat( string, " " );
        j = strlen( string );

        // insert the ASCII value of the symbol plotted with plpoin()

        string[j]     = i + OFFSET;
        string[j + 1] = '\0';

        // plot the string

        plmtex( "rv", 1., 1. - (double) ( i + 1 ) / ( M + 1 ), 0., string );
    }

//  Tell plplot we are done with this page.

    pladv( 0 );                   // advance page

// Don't forget to call plend() to finish off!

    plend();
    exit( 0 );
}

static int
error( char *str )
{
    fprintf( stderr, "%s\n", str );
    exit( 1 );
}