Elementwise minimum of arrays.

def minimum(attrs, inputs, proto_obj):
    """Elementwise minimum of arrays."""
    # MXNet minimum compares only two symbols at a time.
    # ONNX can send more than two to compare.
    # Breaking into multiple mxnet ops to compare two symbols at a time
    if len(inputs) > 1:
        mxnet_op = symbol.minimum(inputs[0], inputs[1])
        for op_input in inputs[2:]:
            mxnet_op = symbol.minimum(mxnet_op, op_input)
    else:
        mxnet_op = symbol.minimum(inputs[0], inputs[0])
    return mxnet_op, attrs, inputs