Hi,

Hopefully this is obvous to someone more familiar with the new ode interface.

I’ve worked through the examples provided by Upgrading to the new ODE interface but i’m still struggling to quite figure out what i’m doing wrong,

I’ve clearly got the types incorrect for the ode call, but I can’t see how?

I’ve simplifed a state-space model right down to what you see below.

I’m using cmdstan v2.26.1 / cmdstanr

the error is:

```
-------------------------------------------------
36: for(i in 2:N){
37: // expects vector[] = ode_rk45(Func, vector y0, real t0, real[] times, )
38: C[i] = ode_rk45(predict, C[i-1], t0, dt[1], kw_obs, Csat);
^
39: }
40: }
-------------------------------------------------
Ill-typed arguments supplied to function 'ode_rk45'. Expected arguments:
(real, vector) => vector, vector, real, real[]
Instead supplied arguments of incompatible type:
(real, vector, real, real) => vector, real, real, real, vector, real
```

What the ode should be doing is predicting the value for `C`

at each time-step, the time-step can be variable hence the length of `dt`

.

```
functions {
vector predict(real t,
vector y,
real kw,
real Csat){
vector[1] dydt;
dydt[1] = kw * (Csat - y[1]);
return dydt;
}
}
data {
int<lower=2> N;
vector[N] C_obs; // SML oxygen concentration (mmol m-3)
vector[N] C_obs_error; // SML oxygen concentration error(mmol m-3)
vector[N] kw_obs; // m s-1
vector[N] Csat_obs; // SML Csat (mmol m-3)
real dt[N];
}
transformed data{
real t0 = 0;
}
parameters {
real init_C;
real Csat;
}
transformed parameters {
vector[N] C; // latent state
C[1] = init_C;
// state model (no process error)
for(i in 2:N){
// expects vector[] = ode_rk45(Func, vector y0, real t0, real[] times, )
C[i] = ode_rk45(predict, C[i-1], t0, dt[i-1], kw_obs, Csat);
}
}
model {
// priors
Csat ~ normal(1, 1);
init_C ~ normal(C_obs[1], C_obs_error[1]);
// measurements
C_obs ~ normal(C, C_obs_error);
}
```