libplplot-dev 5.9.9-2ubuntu2 / usr / share / doc / libplplot11 / examples / c++ / x22.cc

//--------------------------------------------------------------------------
// $Id: x22.cc 11629 2011-03-16 09:32:29Z andrewross $
//    Simple vector plot example
//--------------------------------------------------------------------------
//
//--------------------------------------------------------------------------
// Copyright (C) 2004  Andrew Ross <andrewross@users.sourceforge.net>
//
// This file is part of PLplot.
//
// PLplot is free software; you can redistribute it and/or modify
// it under the terms of the GNU Library General Public License as published by
// the Free Software Foundation; version 2 of the License.
//
// PLplot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public License
// along with PLplot; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
//--------------------------------------------------------------------------
//
//--------------------------------------------------------------------------
// Implementation of PLplot example 22 in C++.
//--------------------------------------------------------------------------

#include "plc++demos.h"

#ifdef PL_USE_NAMESPACE
using namespace std;
#endif

class x22 {
public:
    x22( int, const char ** );

private:
    void circulation();
    void constriction();
    void potential();
    void f2mnmx( PLFLT **f, PLINT nx, PLINT ny, PLFLT *fmin, PLFLT *fmax );

    PLFLT MIN( PLFLT x, PLFLT y ) { return ( x < y ? x : y ); };
    PLFLT MAX( PLFLT x, PLFLT y ) { return ( x > y ? x : y ); };

    plstream *pls;

    PLFLT    **u, **v;
    PLcGrid2 cgrid2;
    int      nx, ny;
};

// Vector plot of the circulation about the origin
void
x22::circulation()
{
    int   i, j;
    PLFLT dx, dy, x, y;
    PLFLT xmin, xmax, ymin, ymax;

    dx = 1.0;
    dy = 1.0;

    xmin = -nx / 2 * dx;
    xmax = nx / 2 * dx;
    ymin = -ny / 2 * dy;
    ymax = ny / 2 * dy;


    // Create data - cirulation around the origin.
    for ( i = 0; i < nx; i++ )
    {
        for ( j = 0; j < ny; j++ )
        {
            x = ( i - nx / 2 + 0.5 ) * dx;
            y = ( j - ny / 2 + 0.5 ) * dy;
            cgrid2.xg[i][j] = x;
            cgrid2.yg[i][j] = y;
            u[i][j]         = y;
            v[i][j]         = -x;
        }
    }

    // Plot vectors with default arrows
    pls->env( xmin, xmax, ymin, ymax, 0, 0 );
    pls->lab( "(x)", "(y)", "#frPLplot Example 22 - circulation" );
    pls->col0( 2 );
    pls->vect( u, v, nx, ny, 0.0, plstream::tr2, (void *) &cgrid2 );
    pls->col0( 1 );
}

// Vector plot of flow through a constricted pipe
void
x22::constriction()
{
    int   i, j;
    PLFLT dx, dy, x, y;
    PLFLT xmin, xmax, ymin, ymax;
    PLFLT Q, b, dbdx;

    dx = 1.0;
    dy = 1.0;

    xmin = -nx / 2 * dx;
    xmax = nx / 2 * dx;
    ymin = -ny / 2 * dy;
    ymax = ny / 2 * dy;

    Q = 2.0;
    for ( i = 0; i < nx; i++ )
    {
        for ( j = 0; j < ny; j++ )
        {
            x = ( i - nx / 2 + 0.5 ) * dx;
            y = ( j - ny / 2 + 0.5 ) * dy;
            cgrid2.xg[i][j] = x;
            cgrid2.yg[i][j] = y;
            b = ymax / 4.0 * ( 3 - cos( M_PI * x / xmax ) );
            if ( fabs( y ) < b )
            {
                dbdx = ymax / 4.0 * sin( M_PI * x / xmax ) *
                       y / b;
                u[i][j] = Q * ymax / b;
                v[i][j] = dbdx * u[i][j];
            }
            else
            {
                u[i][j] = 0.0;
                v[i][j] = 0.0;
            }
        }
    }

    pls->env( xmin, xmax, ymin, ymax, 0, 0 );
    pls->lab( "(x)", "(y)", "#frPLplot Example 22 - constriction" );
    pls->col0( 2 );
    pls->vect( u, v, nx, ny, -0.5, plstream::tr2, (void *) &cgrid2 );
    pls->col0( 1 );
}

// Vector plot of the gradient of a shielded potential (see example 9)
void
x22::potential()
{
    const int nper   = 100;
    const int nlevel = 10;

    int       i, j, nr, ntheta;
    PLFLT     eps, q1, d1, q1i, d1i, q2, d2, q2i, d2i;
    PLFLT     div1, div1i, div2, div2i;
    PLFLT     **z, r, theta, x, y, dz;
    PLFLT     xmin, xmax, ymin, ymax, rmax, zmax, zmin;
    PLFLT     px[nper], py[nper], clevel[nlevel];

    nr     = nx;
    ntheta = ny;

    // Create data to be plotted
    pls->Alloc2dGrid( &z, nr, ntheta );

    // Potential inside a conducting cylinder (or sphere) by method of images.
    // Charge 1 is placed at (d1, d1), with image charge at (d2, d2).
    // Charge 2 is placed at (d1, -d1), with image charge at (d2, -d2).
    // Also put in smoothing term at small distances.

    rmax = (double) nr;

    eps = 2.;

    q1 = 1.;
    d1 = rmax / 4.;

    q1i = -q1 * rmax / d1;
    d1i = pow( (double) rmax, 2. ) / d1;

    q2 = -1.;
    d2 = rmax / 4.;

    q2i = -q2 * rmax / d2;
    d2i = pow( (double) rmax, 2. ) / d2;

    for ( i = 0; i < nr; i++ )
    {
        r = 0.5 + (double) i;
        for ( j = 0; j < ntheta; j++ )
        {
            theta           = 2. * M_PI / ( ntheta - 1 ) * ( 0.5 + (double) j );
            x               = r * cos( theta );
            y               = r * sin( theta );
            cgrid2.xg[i][j] = x;
            cgrid2.yg[i][j] = y;
            div1            = sqrt( pow( (double) ( x - d1 ), 2. ) + pow( (double) ( y - d1 ), 2. ) + pow( (double) eps, 2. ) );
            div1i           = sqrt( pow( (double) ( x - d1i ), 2. ) + pow( (double) ( y - d1i ), 2. ) + pow( (double) eps, 2. ) );
            div2            = sqrt( pow( (double) ( x - d2 ), 2. ) + pow( (double) ( y + d2 ), 2. ) + pow( (double) eps, 2. ) );
            div2i           = sqrt( pow( (double) ( x - d2i ), 2. ) + pow( (double) ( y + d2i ), 2. ) + pow( (double) eps, 2. ) );
            z[i][j]         = q1 / div1 + q1i / div1i + q2 / div2 + q2i / div2i;
            u[i][j]         = -q1 * ( x - d1 ) / pow( (double) div1, 3. ) - q1i * ( x - d1i ) / pow( (double) div1i, 3.0 )
                              - q2 * ( x - d2 ) / pow( (double) div2, 3. ) - q2i * ( x - d2i ) / pow( (double) div2i, 3. );
            v[i][j] = -q1 * ( y - d1 ) / pow( (double) div1, 3. ) - q1i * ( y - d1i ) / pow( (double) div1i, 3.0 )
                      - q2 * ( y + d2 ) / pow( (double) div2, 3. ) - q2i * ( y + d2i ) / pow( (double) div2i, 3. );
        }
    }

    f2mnmx( cgrid2.xg, nr, ntheta, &xmin, &xmax );
    f2mnmx( cgrid2.yg, nr, ntheta, &ymin, &ymax );
    f2mnmx( z, nr, ntheta, &zmin, &zmax );

    pls->env( xmin, xmax, ymin, ymax, 0, 0 );
    pls->lab( "(x)", "(y)", "#frPLplot Example 22 - potential gradient vector plot" );
    // Plot contours of the potential
    dz = ( zmax - zmin ) / (double) nlevel;
    for ( i = 0; i < nlevel; i++ )
    {
        clevel[i] = zmin + ( (double) i + 0.5 ) * dz;
    }
    pls->col0( 3 );
    pls->lsty( 2 );
    pls->cont( z, nr, ntheta, 1, nr, 1, ntheta, clevel, nlevel, plstream::tr2, (void *) &cgrid2 );
    pls->lsty( 1 );
    pls->col0( 1 );

    // Plot the vectors of the gradient of the potential
    pls->col0( 2 );
    pls->vect( u, v, nr, ntheta, 25.0, plstream::tr2, (void *) &cgrid2 );
    pls->col0( 1 );

    // Plot the perimeter of the cylinder
    for ( i = 0; i < nper; i++ )
    {
        theta = ( 2. * M_PI / ( nper - 1 ) ) * (double) i;
        px[i] = rmax * cos( theta );
        py[i] = rmax * sin( theta );
    }
    pls->line( nper, px, py );

    pls->Free2dGrid( z, nr, ntheta );
}

void
x22::f2mnmx( PLFLT **f, PLINT nx, PLINT ny, PLFLT *fmin, PLFLT *fmax )
{
    int i, j;

    *fmax = f[0][0];
    *fmin = *fmax;

    for ( i = 0; i < nx; i++ )
    {
        for ( j = 0; j < ny; j++ )
        {
            *fmax = MAX( *fmax, f[i][j] );
            *fmin = MIN( *fmin, f[i][j] );
        }
    }
}


x22::x22( int argc, const char ** argv )
{
    PLINT narr;
    bool  fill;

    // Set of points making a polygon to use as the arrow
    PLFLT arrow_x[6]  = { -0.5, 0.5, 0.3, 0.5, 0.3, 0.5 };
    PLFLT arrow_y[6]  = { 0.0, 0.0, 0.2, 0.0, -0.2, 0.0 };
    PLFLT arrow2_x[6] = { -0.5, 0.3, 0.3, 0.5, 0.3, 0.3 };
    PLFLT arrow2_y[6] = { 0.0, 0.0, 0.2, 0.0, -0.2, 0.0 };


    // Create new plstream
    pls = new plstream();

    // Parse and process command line arguments

    pls->parseopts( &argc, argv, PL_PARSE_FULL );

    // Initialize plplot

    pls->init();

    nx = 20;
    ny = 20;

    // Allocate arrays
    pls->Alloc2dGrid( &cgrid2.xg, nx, ny );
    pls->Alloc2dGrid( &cgrid2.yg, nx, ny );
    pls->Alloc2dGrid( &u, nx, ny );
    pls->Alloc2dGrid( &v, nx, ny );

    cgrid2.nx = nx;
    cgrid2.ny = ny;

    circulation();

    narr = 6;
    fill = false;

    // Set arrow style using arrow_x and arrow_y then
    // plot using these arrows.
    pls->svect( arrow_x, arrow_y, narr, fill );
    constriction();

    // Set arrow style using arrow2_x and arrow2_y then
    // plot using these filled arrows.
    fill = true;
    pls->svect( arrow2_x, arrow2_y, narr, fill );
    constriction();

    potential();

    pls->Free2dGrid( cgrid2.xg, nx, ny );
    pls->Free2dGrid( cgrid2.yg, nx, ny );
    pls->Free2dGrid( u, nx, ny );
    pls->Free2dGrid( v, nx, ny );

    delete pls;
    exit( 0 );
}

int main( int argc, const char ** argv )
{
    x22 *x = new x22( argc, argv );
    delete x;
}


//--------------------------------------------------------------------------
//                              End of x22.cc
//--------------------------------------------------------------------------