Update multivariate.py

Author: bwalters13

pymc/distributions/multivariate.py

@@ -304,7 +304,7 @@ def rng_fn(cls, rng, alpha, mu, cov, size):
         delta = (1/ np.sqrt(1 + aCa)) * cov @ alpha
         cov_star = np.block([[np.ones(1), delta],
                         [delta[:, None], cov]])
-        mv_samples = multivariate_normal.rng_fn(rng=rng, mean=np.zeros_like(len(mu) + 1), cov=cov_star, size=size)
+        mv_samples = multivariate_normal.rng_fn(rng=rng, mean=np.zeros((mu.shape + 1).eval()), cov=cov_star, size=size)
 
         x0 = mv_samples[:, 0]
         x1 = mv_samples[:, 1:]