woud like to find H(x)

just for one of definition H(x) + H(y) = H(x+y), but it seems require to duplicate one more set of differential system

Error, (in dsolve) found differentiated functions with same name but depending on different arguments in the given DE system: [{a(x), a(y)}, {b(x), b(y)}]

eq2a := a(x)*(diff(c(x), x))+b(x);
eq3a := a(x)*(diff(b(x), x))+c(x)*(diff(b(x), x));
eq4a := a(x)*(diff(c(x), x))+a(x)*(diff(b(x), x))+b(x);
eq2b := a(y)*(diff(c(y), y))+b(y);
eq3b := a(y)*(diff(b(y), y))+c(y)*(diff(b(y), y));
eq4b := a(y)*(diff(c(y), y))+a(y)*(diff(b(y), y))+b(y);
inis := diff(a(x),x)=H(a(x)), diff(b(x),x)=H(b(x)), diff(c(x),x)=H(c(x)), a(1) = b(1), b(1) = c(1), a(0) = b(0), b(0) = c(0);
inis := diff(a(x),x)=H(a(x)), diff(b(x),x)=H(b(x)), diff(c(x),x)=H(c(x));
inio := diff(a(y),y)=H(a(y)), diff(b(y),y)=H(b(y)), diff(c(y),y)=H(c(y)),H(a(x)) + H(b(x)) = H(a(x)+b(x));
sol := dsolve([eq2a=1, eq3a=exp(a), eq4a=0, eq2b=1, eq3b=exp(b), eq4b=0, inis, inio], [a(x), b(x), c(x), a(y), b(y), c(y), H(a(x)), H(b(x)), H(a(y)), H(b(y))]);

aa3 := Normalize(<<aa2[1,1],aa2[2,1],aa2[3,1]>,<aa2[1,2],aa2[2,2],aa2[3,2]>,<aa2[1,3],aa2[2,3],aa2[3,3]>>, Euclidean);

the result is one column

how to normalize to a matrix form?

how to field plot this system?

restart;
with(Physics[Vectors]);
with(DEtools);
with(VectorCalculus);
eq2 := ...;
eq3 := ...;
eq4 := ...;
with(DynamicSystems);
sys := DiffEquation([eq2 = t, eq3 = t], inputvariable = [b(t)], outputvariable = [a(t), c(t)]);
ts := .1;
in_t := t;
sol := Simulate(sys, [in_t]);

with(DEtools):
dfieldplot([...],[a(t),b(t),c(t)],t=−2..2,a=−1..2,b=−1..2,c=−1..2,arrows=SLIM,color=black,dirfield=[10,10]);

@Carl Love 

i guess that it is this.

actually my goal is 

drawing

 tangent vector field on even-dimensional n-spheres

can vector field plot do this too?

if start from draw vector field on a sphere

i find that intersectplot under plot, 

is it possible for fieldplot has this

such as the graph in wiki

https://en.wikipedia.org/wiki/Hairy_ball_theorem

how draw a line x+y = 1 on a sphere x^2+y^2+z^2 = 1 in maple