2.1.21 Clairaut equation. \(x u_x + y u_y + \frac {1}{2} ( (u_x)^2+ (u_y)^2 ) = 0\) with \(u(x,0)= \frac {1}{2} (1-x^2)\)

problem number 21

Taken from Mathematica Symbolic PDE document

Clairaut equation with initial value

Solve for \(u(x,y)\) \[ x u_x + y u_y + \frac {1}{2} ( (u_x)^2+ (u_y)^2 ) = 0 \] With \(u(x,0)= \frac {1}{2} (1-x^2)\)

Mathematica

ClearAll["Global`*"]; 
pde =  u[x, y] == x*D[u[x, y], {x}] + y*D[u[x, y], {y}] + (1/2)*(D[u[x, y], {x}]^2 + D[u[x, y], {y}]^2); 
ic  = u[x, 0] == (1*(1 - x^2))/2; 
sol =  AbsoluteTiming[TimeConstrained[DSolve[{pde, ic}, u[x, y], {x, y}], 60*10]];
 

\[\left \{\left \{u(x,y)\to -\frac {x^2}{2}+y+\frac {1}{2}\right \}\right \}\]

Maple

restart; 
interface(showassumed=0); 
pde := x*diff(u(x, y), x) + y*diff(u(x, y),y) + 1/2 * ( diff(u(x, y), x)^2 + diff(u(x, y), y)^2)=0; 
ic  := u(x,0)=1/2*(1-x^2); 
cpu_time := timelimit(60*10,CodeTools[Usage](assign('sol',pdsolve([pde,ic],u(x,y))),output='realtime'));
 

\begin {align*} & u \left (x , y\right ) = -\frac {\left (x -y +1\right ) \left (x -y -1\right )}{2}\\& u \left (x , y\right ) = -\frac {\left (x +y +1\right ) \left (x +y -1\right )}{2}\\ \end {align*}

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