这与这个问题有关。我设法充分利用了代码,除了一件奇怪的事情。
这是修改后的代码。
import jax.numpy as jnp
from jax import grad, jit, value_and_grad
from jax import vmap, pmap
from jax import random
import jax
from jax import lax
from jax import custom_jvp
def p_tau(z, tau, alpha=1.5):
return jnp.clip((alpha - 1) * z - tau, a_min=0) ** (1 / (alpha - 1))
def get_tau(tau, tau_max, tau_min, z_value):
return lax.cond(z_value < 1,
lambda _: (tau, tau_min),
lambda _: (tau_max, tau),
operand=None
)
def body(kwargs, x):
tau_min = kwargs['tau_min']
tau_max = kwargs['tau_max']
z = kwargs['z']
alpha = kwargs['alpha']
tau = (tau_min + tau_max) / 2
z_value = p_tau(z, tau, alpha).sum()
taus = get_tau(tau, tau_max, tau_min, z_value)
tau_max, tau_min = taus[0], taus[1]
return {'tau_min': tau_min, 'tau_max': tau_max, 'z': z, 'alpha': alpha}, None
@jax.partial(jax.jit, static_argnums=(2,))
def map_row(z_input, alpha, T):
z = (alpha - 1) * z_input
tau_min, tau_max = jnp.min(z) - 1, jnp.max(z) - z.shape[0] ** (1 - alpha)
result, _ = lax.scan(body, {'tau_min': tau_min, 'tau_max': tau_max, 'z': z, 'alpha': alpha}, xs=None,
length=T)
tau = (result['tau_max'] + result['tau_min']) / 2
result = p_tau(z, tau, alpha)
return result / result.sum()
@jax.partial(jax.jit, static_argnums=(1,3,))
def _entmax(input, axis=-1, alpha=1.5, T=20):
result = vmap(jax.partial(map_row, alpha=alpha, T=T), axis)(input)
return result
@jax.partial(custom_jvp, nondiff_argnums=(1, 2, 3,))
def entmax(input, axis=-1, alpha=1.5, T=10):
return _entmax(input, axis, alpha, T)
@jax.partial(jax.jit, static_argnums=(0,2,))
def _entmax_jvp_impl(axis, alpha, T, primals, tangents):
input = primals[0]
Y = entmax(input, axis, alpha, T)
gppr = Y ** (2 - alpha)
grad_output = tangents[0]
dX = grad_output * gppr
q = dX.sum(axis=axis) / gppr.sum(axis=axis)
q = jnp.expand_dims(q, axis=axis)
dX -= q * gppr
return Y, dX
@entmax.defjvp
def entmax_jvp(axis, alpha, T, primals, tangents):
return _entmax_jvp_impl(axis, alpha, T, primals, tangents)
import numpy as np
input = jnp.array(np.random.randn(64, 10)).block_until_ready()
weight = jnp.array(np.random.randn(64, 10)).block_until_ready()
def toy(input, weight):
return (weight*entmax(input, axis=0, alpha=1.5, T=20)).sum()
jax.jit(value_and_grad(toy))(input, weight)
此代码将产生如下错误:
tuple index out of range
这是由这行代码引起的
@jax.partial(jax.jit, static_argnums=(2,))
def map_row(z_input, alpha, T):
即使我只用实体函数替换函数体,错误仍然存在。这是一个非常奇怪的行为。但是,让这个东西保持静态对我来说非常重要,因为它有助于展开循环。