> restart; > with(DEtools); [AreSimilar, DEnormal, DEplot, DEplot3d, DEplot_polygon, DFactor, DFactorLCLM, DFactorsols, Dchangevar, FunctionDecomposition, GCRD, Gosper, Heunsols, Homomorphisms, IsHyperexponential, LCLM, MeijerGsols, MultiplicativeDecomposition, ODEInvariants, PDEchangecoords, PolynomialNormalForm, RationalCanonicalForm, ReduceHyperexp, RiemannPsols, Xchange, Xcommutator, Xgauge, Zeilberger, abelsol, adjoint, autonomous, bernoullisol, buildsol, buildsym, canoni, caseplot, casesplit, checkrank, chinisol, clairautsol, constcoeffsols, convertAlg, convertsys, dalembertsol, dcoeffs, de2diffop, dfieldplot, diff_table, diffop2de, dperiodic_sols, dpolyform, dsubs, eigenring, endomorphism_charpoly, equinv, eta_k, eulersols, exactsol, expsols, exterior_power, firint, firtest, formal_sol, gen_exp, generate_ic, genhomosol, gensys, hamilton_eqs, hypergeomsols, hyperode, indicialeq, infgen, initialdata, integrate_sols, intfactor, invariants, kovacicsols, leftdivision, liesol, line_int, linearsol, matrixDE, matrix_riccati, maxdimsystems, moser_reduce, muchange, mult, mutest, newton_polygon, normalG2, ode_int_y, ode_y1, odeadvisor, odepde, parametricsol, particularsol, phaseportrait, poincare, polysols, power_equivalent, rational_equivalent, ratsols, redode, reduceOrder, reduce_order, regular_parts, regularsp, remove_RootOf, riccati_system, riccatisol, rifread, rifsimp, rightdivision, rtaylor, separablesol, singularities, solve_group, super_reduce, symgen, symmetric_power, symmetric_product, symtest, transinv, translate, untranslate, varparam, zoom] > sys:=diff(x(t),t)=(2*(x(t))^2+3*x(t)+1)/y(t),diff(y(t),t)=-2*x(t)-2; 2 d 2 x(t) + 3 x(t) + 1 d sys := -- x(t) = --------------------, -- y(t) = -2 x(t) - 2 dt y(t) dt > ic:=x(1)=-2/3,y(1)=-3/2; ic := x(1) = -2/3, y(1) = -3/2 > dsolve([sys,ic]); > DEplot( [sys], [x(t),y(t)], t=-60..40, x=-1..-0.5, y=-35..1, > [[ic]], arrows=medium); > ed:=diff(y(t),t)=-1/y(t)/2-1; d 1 ed := -- y(t) = -1/2 ---- - 1 dt y(t) > ic1:=y(1)=-3/2; ic1 := y(1) = -3/2 > yy:=subs(dsolve([ed,ic1],y(t)),y(t)); yy := - 1/2 - 1/2 LambertW(-2 exp(-I (2 I t - Pi))) > xx:=-1/2+1/4/yy; 1 xx := - 1/2 + 1/4 --------------------------------------------- - 1/2 - 1/2 LambertW(-2 exp(-I (2 I t - Pi))) > plot([xx,yy,t=-60..40]); > series(yy,t=0); LambertW(2) LambertW(2) (- 1/2 - 1/2 LambertW(2)) - --------------- t - ------------------ 1 + LambertW(2) 3 (1 + LambertW(2)) 2 LambertW(2) (2 LambertW(2) - 1) 3 t + 2/3 ------------------------------- t - 5 (1 + LambertW(2)) 2 LambertW(2) (-8 LambertW(2) + 6 LambertW(2) + 1) 4 1/3 ------------------------------------------------- t + 7 (1 + LambertW(2)) 2/15 LambertW(2) 2 3 / (22 LambertW(2) - 1 - 58 LambertW(2) + 24 LambertW(2) ) / / 9 5 6 (1 + LambertW(2)) t + O(t ) >