sigm.py 文件源码

def is_1pexp(t, only_process_constants=True):
    """

    Returns
    -------
    object
        If 't' is of the form (1+exp(x)), return (False, x).
        Else return None.

    """
    if t.owner and t.owner.op == tensor.add:
        scalars, scalar_inputs, nonconsts = \
            opt.scalarconsts_rest(t.owner.inputs,
                                  only_process_constants=only_process_constants)
        # scalar_inputs are potentially dimshuffled and filled with scalars
        if len(nonconsts) == 1:
            maybe_exp = nonconsts[0]
            if maybe_exp.owner and maybe_exp.owner.op == tensor.exp:
                # Verify that the constant terms sum to 1.
                if scalars:
                    scal_sum = scalars[0]
                    for s in scalars[1:]:
                        scal_sum = scal_sum + s
                    if numpy.allclose(scal_sum, 1):
                        return False, maybe_exp.owner.inputs[0]
                # Before 7987b51 there used to be a bug where *any* constant
                # was considered as if it was equal to 1, and thus this
                # function would incorrectly identify it as (1 + exp(x)).
                if config.warn.identify_1pexp_bug:
                    warnings.warn(
                        'Although your current code is fine, please note that '
                        'Theano versions prior to 0.5 (more specifically, '
                        'prior to commit 7987b51 on 2011-12-18) may have '
                        'yielded an incorrect result. To remove this warning, '
                        'either set the `warn.identify_1pexp_bug` config '
                        'option to False, or `warn.ignore_bug_before` to at '
                        'least \'0.4.1\'.')
    return None