Ode_rk45 solving for only one time point

General
1

Dear all,
I am trying to solve an ODE at one time point T1 in future hence I feed a single value of solution time to the integrator by:
real T1 = times[i];
however I got data type error:

Semantic error in ‘string’, line 48, column 9 to column 51:
Ill-typed arguments supplied to function ‘ode_rk45’. Expected arguments:
(real, vector) => vector, vector, real, real[]
Instead supplied arguments of incompatible type:
(real, vector, vector) => vector, vector, real, real, vector

Then I tried to define an array of length 1 for solution time by this command:
array[1] real T1 = times[i];
but I failed to assign a real value to this array:

Semantic error in ‘string’, line 47, column 4 to column 32:
Ill-typed arguments supplied to assignment operator =: lhs has type real[] and rhs has type real

Here is my stan code:

functions{
    vector PK3cmt(real t, vector states, vector theta){
    real ka = theta[1];
    real CL = theta[2];
    real Vc = theta[3]; 
    real Q = theta[4]; 
    real Vp = theta[5]; 
    real gut = states[1];
    real cent = states[2]; 
    real peri = states[3];
    vector[3] dif; 
    dif[1] = - ka * gut;
    dif[2] = -ka*gut - ((CL / Vc) + (Q / Vc))*cent + (Q * peri) / Vp; 
    dif[3] = (Q*cent)/ Vc - (Q*peri)/Vp; 
    return dif; 
    }
}
data{
    int N; 
    //vector<lower = 0>[N] time; 
    array[N] real times; 
    int evid[N]; 
    int cmt[N]; 
    vector<lower = 0>[N] amt; 
    int nObs; 
    int iObs[nObs]; 
    vector<lower=0>[N] cObs; 
}
transformed data {
  int nTheta = 5;
  int nCmt = 3;
}
parameters{
  vector[nTheta] theta; //{ka, CL, Vc, Q, Vp}
  real<lower = 0> sigma;
}
transformed parameters{
  vector[nCmt] U; 
  U[1] = 0; 
  U[2] = 0; 
  U[3] = 0; 
  array[N] vector[3] traj;
  for(i in 1:N){
    if (evid[i] == 1) U[cmt[i]] += amt[i];
    else {
    //real T1 = times[i];   // doesn't work
    array[1] real T1 = times[i];  // also doesn't work 
     U = ode_rk45(PK3cmt, U, times[i-1], T1, theta);
    traj[i] = U;
    }
  }
 vector<lower=0>[N] concentrationHat = traj[][2] ./theta[3];
}
model{
  theta[2] ~ lognormal(log(10), 0.25); 
  theta[4] ~ lognormal(log(15), 0.5);
  theta[3] ~ lognormal(log(35), 0.25);
  theta[5] ~ lognormal(log(105), 0.5);
  theta[1] ~ lognormal(log(2.5), 1);
  sigma ~ normal(0, 1);
  cObs ~ lognormal(log(concentrationHat[iObs]), sigma);
}

Any help is apprecaited.
Hassan

2

This would need to be array[1] real T1 = {times[i]};

There seem to be more errors after fixing this, but they seem more related to the structure of your model so it’s less clear to me what solution to recommend

3

Thanks a lot, it fixed my problem. :)