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differential equations - DSolve and coupled linear first order PDEs


Does any one know a trick to make DSolve find solution to this coupled linear first order PDE system: (these are Cauchy-Riemann PDE equations, but with one of them having one of the dependent variables as well).


ClearAll[F1,F2,x,y];

ode1 = D[F1[x,y],y]-D[F2[x,y],x] == 0
ode2 = D[F1[x,y],x]+D[F2[x,y],y] == y (*y here causes the problem*)

DSolve[{ode1,ode2},{F1[x,y],F2[x,y]},{x,y}]


Mathematica graphics


This can be solved in Maple:


restart;
#infolevel[pdsolve]:=3;
eq1:= diff(F1(x,y),y)-diff(F2(x,y),x) = 0;
eq2:= diff(F1(x,y),x)+diff(F2(x,y),y) = y;
pdsolve({eq1,eq2},{F1(x,y),F2(x,y)});

Solution it gives is



F1(x, y) = _F1(y-I*x)+_F2(y+I*x)
F2(x, y) = I*_F1(y-I*x)-I*_F2(y+I*x)+(1/2)*y^2+_C1

Screen shot:


Mathematica graphics


If the RHS of the second equation is not y but a constant or some other parameter, then Mathematica can now solve it:


ClearAll[F1,F2,x,y,m];
ode1 = D[F1[x,y],y]-D[F2[x,y],x] == 0
ode2 = D[F1[x,y],x]+D[F2[x,y],y] == m
DSolve[{ode1,ode2},{F1[x,y],F2[x,y]},{x,y}]


Mathematica graphics


Is this a known limitation of DSolve or is there a trick or some other method to get the same solution as in Maple?


Using version 11.2 on windows 7.



Answer



The following substitution eliminates the right side of ode2, and DSolve then can solve the resulting equations.


ode3 = Unevaluated[D[F1[x, y], y] - D[F2[x, y], x] == 0] /. F2[x, y] -> G2[x, y] + y^2/2
(* D[F1[x, y], y] - D[G2[x, y], x] == 0 *)

ode4 = Simplify[Unevaluated[D[F1[x, y], x] + D[F2[x, y], y] == y] /.

F2[x, y] -> G2[x, y] + y^2/2]
(* D[F1[x, y], x] + D[G2[x, y], y] == 0 *)

DSolve[{ode3, ode4}, {F1[x, y], G2[x, y]}, {x, y}] // Flatten
(* {F1[x, y] -> I C[1][I x + y] - I C[2][-I x + y],
G2[x, y] -> C[1][I x + y] + C[2][-I x + y]} *)

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