// Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
// Copyright (C) INRIA
// This file must be used under the terms of the CeCILL.
// This source file is licensed as described in the file COPYING, which
// you should have received as part of this distribution.  The terms
// are also available at
// http://www.cecill.info/licences/Licence_CeCILL_V2.1-en.txt

function []=fchamp(macr_f,fch_t,fch_xr,fch_yr,arfact,rect,strf)
    //   Draw vector field in R^2,
    //   Vector field defined by:
    //   y=f(x,t,[u]), for compatibility with ode function
    //    f : vector field. CAn be either :
    //	 a function y=f(t,x,[u])
    //       a list such as  list(f1,u1) with f1 a function
    //       y=f1(t,x,u) and u1=current value of u
    //    t : instants vector
    //    xr,yr: two vectors defining the gridding
    //    arfact : optional arg to control size of arrow heads,
    //    strf : string ( same as  plot2d )
    //Example : enter fchamp()
    //!

    [lhs,rhs]=argn(0)
    if rhs <= 0 then   // demo
        deff("[xdot] = derpol(t,x)",["xd1 = x(2)"; ..
        "xd2 = -x(1) + (1 - x(1)**2)*x(2)"; ..
        "xdot = [ xd1 ; xd2 ]"]);
        fchamp(derpol,0,-1:0.1:1,-1:0.1:1,1);
        return
    end

    if rhs <= 1,fch_t=0;end
    if rhs <= 2,fch_xr=-1:0.1:1;end
    if rhs <= 3,fch_yr=-1:0.1:1;end

    opts=[]
    if exists("arfact","local")==1 then opts=[opts,"arfact=arfact"],end
    if exists("rect","local")==1 then opts=[opts,"rect=rect"],end
    if exists("strf","local")==1 then opts=[opts,"strf=strf"],end

    if type(macr_f) <> 15,
        if type(macr_f)==11 then comp(macr_f),end;
        deff("[yy]=mmm(x1,x2)",["xx=macr_f(fch_t,[x1;x2])";"yy=xx(1)+%i*xx(2);"]);
    else
        mmm1=macr_f(1)
        if type(mmm1)==11 then comp(mmm1),end;
        deff("[yy]=mmm(x1,x2)",["xx=mmm1(fch_t,[x1;x2],macr_f(2));";
        "yy=xx(1)+%i*xx(2);"]);
    end
    fch_v=feval(fch_xr,fch_yr,mmm);


    execstr("champ(fch_xr,fch_yr,real(fch_v),imag(fch_v),"+strcat(opts,",")+")")
endfunction