Polynomial regression gives wrong results (?)

Hi RapidMiner,

I'm trying to use Polynomial Regression with a dataset generated from the function: y= 2*x^2 + 3*x + 1, and test the model with the same dataset, but the prediction results look like a straight line (attached picture). All the parameters are set as default (max iterations= 5000, replication factor= 1, max degree= 5). Could you show me how to get the correct result which can capture the quadratic curve using Polynomial Regression? I paste the dataset below and also insert the process code at the end. Thank you very much!

x y
1 6
2 15
3 28
4 45
5 66
6 91
7 120
8 153
9 190
10 231
11 276
12 325
13 378
14 435
15 496
16 561
17 630
18 703
19 780
20 861
21 946
22 1035
23 1128
24 1225

<?xml version="1.0" encoding="UTF-8"?><process version="7.3.000">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="7.3.000" expanded="true" name="Process">
    <parameter key="logverbosity" value="init"/>
    <parameter key="random_seed" value="2001"/>
    <parameter key="send_mail" value="never"/>
    <parameter key="notification_email" value=""/>
    <parameter key="process_duration_for_mail" value="30"/>
    <parameter key="encoding" value="SYSTEM"/>
    <process expanded="true">
      <operator activated="true" class="retrieve" compatibility="7.3.000" expanded="true" height="68" name="Retrieve Polynomial" width="90" x="112" y="34">
        <parameter key="repository_entry" value="Polynomial"/>
      </operator>
      <operator activated="true" class="set_role" compatibility="7.3.000" expanded="true" height="82" name="Set Role" width="90" x="246" y="34">
        <parameter key="attribute_name" value="y"/>
        <parameter key="target_role" value="label"/>
        <list key="set_additional_roles"/>
      </operator>
      <operator activated="true" class="normalize" compatibility="7.3.000" expanded="true" height="103" name="Normalize" width="90" x="380" y="34">
        <parameter key="return_preprocessing_model" value="false"/>
        <parameter key="create_view" value="false"/>
        <parameter key="attribute_filter_type" value="single"/>
        <parameter key="attribute" value="x"/>
        <parameter key="attributes" value=""/>
        <parameter key="use_except_expression" value="false"/>
        <parameter key="value_type" value="numeric"/>
        <parameter key="use_value_type_exception" value="false"/>
        <parameter key="except_value_type" value="real"/>
        <parameter key="block_type" value="value_series"/>
        <parameter key="use_block_type_exception" value="false"/>
        <parameter key="except_block_type" value="value_series_end"/>
        <parameter key="invert_selection" value="false"/>
        <parameter key="include_special_attributes" value="false"/>
        <parameter key="method" value="range transformation"/>
        <parameter key="min" value="-1.0"/>
        <parameter key="max" value="1.0"/>
      </operator>
      <operator activated="true" class="polynomial_regression" compatibility="7.3.000" expanded="true" height="82" name="Polynomial Regression" width="90" x="648" y="34">
        <parameter key="max_iterations" value="5000"/>
        <parameter key="replication_factor" value="1"/>
        <parameter key="max_degree" value="5"/>
        <parameter key="min_coefficient" value="-100.0"/>
        <parameter key="max_coefficient" value="100.0"/>
        <parameter key="use_local_random_seed" value="false"/>
        <parameter key="local_random_seed" value="1992"/>
      </operator>
      <operator activated="true" class="retrieve" compatibility="7.3.000" expanded="true" height="68" name="Retrieve Polynomial (2)" width="90" x="112" y="289">
        <parameter key="repository_entry" value="Polynomial"/>
      </operator>
      <operator activated="true" class="set_role" compatibility="7.3.000" expanded="true" height="82" name="Set Role (2)" width="90" x="246" y="289">
        <parameter key="attribute_name" value="y"/>
        <parameter key="target_role" value="label"/>
        <list key="set_additional_roles"/>
      </operator>
      <operator activated="true" class="normalize" compatibility="7.3.000" expanded="true" height="103" name="Normalize (2)" width="90" x="380" y="289">
        <parameter key="return_preprocessing_model" value="false"/>
        <parameter key="create_view" value="false"/>
        <parameter key="attribute_filter_type" value="single"/>
        <parameter key="attribute" value="x"/>
        <parameter key="attributes" value=""/>
        <parameter key="use_except_expression" value="false"/>
        <parameter key="value_type" value="numeric"/>
        <parameter key="use_value_type_exception" value="false"/>
        <parameter key="except_value_type" value="real"/>
        <parameter key="block_type" value="value_series"/>
        <parameter key="use_block_type_exception" value="false"/>
        <parameter key="except_block_type" value="value_series_end"/>
        <parameter key="invert_selection" value="false"/>
        <parameter key="include_special_attributes" value="false"/>
        <parameter key="method" value="range transformation"/>
        <parameter key="min" value="-1.0"/>
        <parameter key="max" value="1.0"/>
      </operator>
      <operator activated="true" class="denormalize" compatibility="7.3.000" expanded="true" height="82" name="De-Normalize" width="90" x="581" y="493">
        <parameter key="missing_attribute_handling" value="proceed on missing"/>
      </operator>
      <operator activated="true" class="apply_model" compatibility="7.3.000" expanded="true" height="82" name="Apply Model" width="90" x="514" y="289">
        <list key="application_parameters"/>
        <parameter key="create_view" value="false"/>
      </operator>
      <operator activated="true" class="apply_model" compatibility="7.3.000" expanded="true" height="82" name="Apply Model (2)" width="90" x="715" y="289">
        <list key="application_parameters"/>
        <parameter key="create_view" value="false"/>
      </operator>
      <connect from_op="Retrieve Polynomial" from_port="output" to_op="Set Role" to_port="example set input"/>
      <connect from_op="Set Role" from_port="example set output" to_op="Normalize" to_port="example set input"/>
      <connect from_op="Normalize" from_port="example set output" to_op="Polynomial Regression" to_port="training set"/>
      <connect from_op="Polynomial Regression" from_port="model" to_op="Apply Model" to_port="model"/>
      <connect from_op="Retrieve Polynomial (2)" from_port="output" to_op="Set Role (2)" to_port="example set input"/>
      <connect from_op="Set Role (2)" from_port="example set output" to_op="Normalize (2)" to_port="example set input"/>
      <connect from_op="Normalize (2)" from_port="example set output" to_op="Apply Model" to_port="unlabelled data"/>
      <connect from_op="Normalize (2)" from_port="preprocessing model" to_op="De-Normalize" to_port="model input"/>
      <connect from_op="De-Normalize" from_port="model output" to_op="Apply Model (2)" to_port="model"/>
      <connect from_op="Apply Model" from_port="labelled data" to_op="Apply Model (2)" to_port="unlabelled data"/>
      <connect from_op="Apply Model (2)" from_port="labelled data" to_port="result 1"/>
      <connect from_op="Apply Model (2)" from_port="model" to_port="result 2"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
      <portSpacing port="sink_result 2" spacing="0"/>
      <portSpacing port="sink_result 3" spacing="0"/>
    </process>
  </operator>
</process>