function  primka(a1,a2,a3,s1,s2,s3)
%primka parametricky v R3
%a1,a2,a3 souradnice bodu leyiciho na p[rimce
%s1,s2,s3 smerovy vektor primky 
%volani primka(1,-2,0,1,1,2)

syms t
x=a1+t*s1;
y=a2+t*s2;
z=a3+t*s3;
ezplot3(x,y,z, [-5 5]) %bod lezi na primce pro t=1

%=========== nepovinne vykresleni bodu na primce

hold on
h=plot3(a1,a2,a3); %plot3 kresli nesymbolicky ve 3D
set(h,'marker','+','markersize',25)