Log likelihood and gradient of the log likelihood of a continuous-time Markov model.
| Parameters: | theta : array of shape = (n*(n-1)/2 + n) for dense or shorter 
 counts : array of shape = (n, n) 
 t : double 
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|---|---|
| Returns: | logl : double 
 grad : array of shape = (n*(n-1)/2 + n) 
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