Question: dsolve formal series

Hello, would you please help with this problem

 I need to solve the system using polynomial coefficients

thank you 




eq1 := diff(A(r), r, r)+(diff(A(r), r))/r+A(r)/r^2-a*r*A(r)+b*r^2*f*B(r)

diff(diff(A(r), r), r)+(diff(A(r), r))/r+A(r)/r^2-a*r*A(r)+b*r^2*f*B(r)


eq2 := diff(B(r), r, r)+(diff(B(r), r))/r+B(r)/r^2-c*r*A(r)+d*r^2*B(r)

diff(diff(B(r), r), r)+(diff(B(r), r))/r+B(r)/r^2-c*r*A(r)+d*r^2*B(r)




dsolve({eq1, eq2}, {A(r), B(r)});

{A(r) = DESol({-(-b*c*f*r^7+a*d*r^7-d*r^4+2*a*r^3-17)*_Y(r)/r^4-(-d*r^5-a*r^4-3*r)*(diff(_Y(r), r))/r^4-(-d*r^6+a*r^5-r^2)*(diff(diff(_Y(r), r), r))/r^4-2*(diff(diff(diff(_Y(r), r), r), r))/r+diff(diff(diff(diff(_Y(r), r), r), r), r)}, {_Y(r)}), B(r) = (a*r^3*A(r)-(diff(diff(A(r), r), r))*r^2-(diff(A(r), r))*r-A(r))/(b*f*r^4)}


dsolve({eq1, eq2}, {A(r), B(r)}, 'formal_series', 'coeffs' = 'polynomial')

Error, (in dsolve/FORMALSERIES) the first argument must be a homogeneous linear ode with polynomial coefficients







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