# Is there a way to specify the dependent variable in eulers_method?

Consider

```
sage: u,v = PolynomialRing(QQ,2, "uv").gens()
sage: eulers_method(2*u + v, 1, 5, 0.2, 4)
```

On the face of it it's ambiguous whether this is solving du/dv = 2*u + v with u(v=1) = 5 or if it's doing dv/du = 2*u + v with v(u=1)=5. In practice it solves the latter, but how is that determined?

It appears to hinge on the order of u and v on the LHS of the first line but I can't find any mention of this in the documentation.

Asking for the code via

`??eulers_method`

and going till the end, we get it and there is an obvious asymmetry in the variables`x0`

and`y0`

,so

`h`

is married with`x0`

.How is the order of the arguments of f determined from the input expression?

The call in the example is:

The arguments above are placed inside the definition as follows:

`f`

becomes`2*u+v`

and`x0`

becomes`1`

, and`y0`

is`5`

, and`h`

is the step`.2`

and we go till`x1`

which is`4`

. The question is now, how we computei.e. why do we get

and not

`11`

. Instead of answering this question, i would prefer to use a proper function in the call. so that there is no such question, depending on hidden structure. For instance:a.s.o.