# Question:Incorrect use of independent variables (PDE)

## Question:Incorrect use of independent variables (PDE)

Maple 16
`restart:with(PDEtools):with(plots):declare(u(x,y,t)):PDE1:=diff(u(x,y,t),t\$1)+a*u(x,y,t)*diff(u(x,y,t),x\$1)+diff(u(x,y,t),x\$3)+`
`b*diff(u(x,y,t),y\$2)=0;Sol1:=pdsolve(PDE1);`
`Test1:=pdetest(Sol1,PDE1);params:={a=6,b=1,_C1=1,_C2=1,_C3=1,_C4=1};`
`Sol2:=subs(params,Sol1);`
`plot3d(subs(t=1,rhs(Sol2)),x=-10..10,y=-10..10,axes=boxed,grid=[50,50],`
`style=patchnogrid,shading=Z,orientation=[-40,50]);`
` `
`Sol3:=[SimilaritySolutions(PDE1,removeredundant=true)];`
`Error, (in PDEtools:-ToJet) incorrect use of independent variables {_phi} in `
`the names of the  dependent variables {_phi[3](_phi[1], _phi[2])}`
`Test2:=map(pdetest,Sol3,PDE1);`
`Error, (in pdetest) unable to determine the indeterminate function`
`Sol4:=combine(subs(params,Sol3));`
`                      plot3d(subs(t=1,rhs(Sol4[3])),x=-10..10,y=-10..10,axes=boxed,grid=[50,50],`
`style=patchnogrid,shading=Z,orientation=[-40,50]);`
`Error, invalid input: rhs received Sol3[3], which is not valid for its 1st argument,`
` exprThanks`
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