gradient_check.py 文件源码

def eval_numerical_gradient_blobs(f, inputs, output, h=1e-5):
    '''
    Compute numeric gradients for a function that operates on input
    and output blobs.

    We assume that f accepts several input blobs as arguments, followed by a blob
    into which outputs will be written. For example, f might be called like this:

    f(x, w, out)

    where x and w are input Blobs, and the result of f will be written to out.

    Inputs:
    - f: function
    - inputs: tuple of input blobs
    - output: output blob
    - h: step size
    '''
    numeric_diffs = []
    for input_blob in inputs:
        diff = np.zeros_like(input_blob.diffs)
        it = np.nditer(input_blob.vals, flags=['multi_index'],
                       op_flags=['readwrite'])
        while not it.finished:
            idx = it.multi_index
            orig = input_blob.vals[idx]

            input_blob.vals[idx] = orig + h
            f(*(inputs + (output,)))
            pos = np.copy(output.vals)
            input_blob.vals[idx] = orig - h
            f(*(inputs + (output,)))
            neg = np.copy(output.vals)
            input_blob.vals[idx] = orig

            diff[idx] = np.sum((pos - neg) * output.diffs) / (2.0 * h)

            it.iternext()
        numeric_diffs.append(diff)
    return numeric_diffs