Hi

I have a problem that has been totally eating me up all day. I believe there is a simple solution to the question…

If I specify a theano shared variable for use in a pymc3 model so that i can loop without re-specifying the model, it seems the initial value of the shared variable effects the result. If the initial value is too far from the new value, I get a “The derivative of RV `test1`

.ravel()[0] is zero.” error. Why is this??

See my code below. changing the nf value to 10 or change the new value to 100000 would fix the error…

def test():

```
nf = 10000000000000000000
sharednf = shared(nf)
with pm.Model() as model:
test = pm.Normal("test"+str(1), mu=sharednf, sd=1**100)
sum = test + 1
pm.Deterministic("sum"+str(1), sum)
for i in range(10):
sharednf.set_value(float(1))
with model:
trace = pm.sample(5000)
trace1 = trace
print(pm.summary(trace))
pm.traceplot(trace)
plt.show()
```