from stan lda example

gistfile1.r

 data {                                                                                                             
   int<lower=2> K;               // num topics                                                                      
   int<lower=2> V;               // num words                                                                       
   int<lower=1> M;               // num docs                                                                        
   int<lower=1> N;               // total word instances                                                            
   int<lower=1,upper=V> w[N];    // word n                                                                          
   int<lower=1,upper=M> doc[N];  // doc ID for word n                                                               
   vector<lower=0>[K] alpha;     // topic prior                                                                     
   vector<lower=0>[V] beta;      // word prior                                                                      
 }                                                                                                                  
 parameters {                                                                                                       
   simplex[K] theta[M];   // topic dist for doc m                                                                   
   simplex[V] phi[K];     // word dist for topic k                                                                  
 }                                                                                                                  
 model {                                                                                                            
   for (m in 1:M)                                                                                                   
     theta[m] ~ dirichlet(alpha);  // prior                                                                         
   for (k in 1:K)                                                                                                   
     phi[k] ~ dirichlet(beta);     // prior                                                                         
   for (n in 1:N) {                                                                                                 
     real gamma[K];                                                                                                 
     for (k in 1:K)                                                                                                 
       gamma[k] <- log(theta[doc[n],k]) + log(phi[k,w[n]]);                                                         
     lp__ <- lp__ + log_sum_exp(gamma);  // likelihood                                                              
   }                                                                                                                
 }