jax.custom_vjp#

class jax.custom_vjp(fun, nondiff_argnums=())[source]#

Set up a JAX-transformable function for a custom VJP rule definition.

This class is meant to be used as a function decorator. Instances are callables that behave similarly to the underlying function to which the decorator was applied, except when a reverse-mode differentiation transformation (like jax.grad()) is applied, in which case a custom user-supplied VJP rule function is used instead of tracing into and performing automatic differentiation of the underlying function’s implementation. There is a single instance method, defvjp(), which may be used to define the custom VJP rule.

This decorator precludes the use of forward-mode automatic differentiation.

For example:

@jax.custom_vjp
def f(x, y):
  return jnp.sin(x) * y

def f_fwd(x, y):
  return f(x, y), (jnp.cos(x), jnp.sin(x), y)

def f_bwd(res, g):
  cos_x, sin_x, y = res
  return (cos_x * g * y, sin_x * g)

f.defvjp(f_fwd, f_bwd)

For a more detailed introduction, see the tutorial.

Parameters
__init__(fun, nondiff_argnums=())[source]#
Parameters

Methods

__init__(fun[, nondiff_argnums])

param fun

defvjp(fwd, bwd)

Define a custom VJP rule for the function represented by this instance.