# Question:Error When using DeterminingPDE

## Question:Error When using DeterminingPDE

Maple

Good Afternoon,

I'm relatively new to using Maple and I have encountered a problem that I don't seem to be able to figure out myself.

I am trying to calculate the determining equations, and subsequently the infinitesimals of an underdetermined set of PDE's. However, I keep getting the error message

"Error, (in PDEtools:-ToJet) incorrect use of the dependent variable name(s) [R, p, u, v, w], as indexed function names in: {w[](R[z]*v[y]+v[z]), w[](R[z]*w[y]+w[z])}"

```restart;
with(PDEtools);
with(DEtools);
declare(u(y, z));
u(y, z) will now be displayed as u

declare(v(y, z));
v(y, z) will now be displayed as v

declare(w(y, z));
w(y, z) will now be displayed as w

declare(p(y, z));
p(y, z) will now be displayed as p

declare(R(z));
R(z) will now be displayed as R

Conti := diff(u(y, z), y) + u(y, z)/(y - R(z)) + diff(w(y, z), z) + diff(R(z), z)*diff(w(y, z), y) = 0;
NSU := v(y, z)^2/(y - R(z)) - diff(p(y, z), y) = 0;
NSV := ((u(y, z)*diff(v(y, z), y) + u(y, z)*v(y, z)/(y - R(z)) + w(y, z)(diff(v(y, z), z) + diff(R(z), z)*diff(v(y, z), y))) + (-diff(v(y, z), y)/(y - R(z)) - diff(v(y, z), y, y) + v(y, z)/(y - R(z))^2)) + diff(R(z), z)*diff(w(y, z), y) = 0;
NSW := u(y, z)*diff(w(y, z), z) + w(y, z)(diff(w(y, z), z) + diff(R(z), z)*diff(w(y, z), y)) + diff(p(y, z), z) + diff(R(z), z)*diff(p(y, z), y) - diff(w(y, z), y)/(y - R(z)) - diff(w(y, z), y, y) - diff(R(z), z)*diff(w(y, z), y) = 0;
sys := [Conti, NSU, NSV, NSW];
deteqs := Infinitesimals(sys);
Error, (in PDEtools:-ToJet) incorrect use of the dependent variable name(s) [R, p, u, v, w], as indexed function names in: {w[](R[z]*v[y]+v[z]), w[](R[z]*w[y]+w[z])}
```

The Maple Worksheet is also provided below. All help is greatly appreciated.

Regards,

Johannes

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