How to post input array values using ajax

Question

Following is html and php codes I am using.

I am going to send input array values using ajax request.

But I don't know how I can get those values in jquery.

How can I send these using ajax?

<div class="tab-pane fade" id="variables">
   <div class="form-group clearfix">
      <div class="box-wt200">
         <select multiple="multiple" id="mul_sel_v1" name="variables[0][]" placeholder="Variable 1" class="multi-select form-control dropdown-variable">
         </select>//I want to send these values via ajax call
         <div class="xyd-inline">
            <div>
               <input type="checkbox" id="x_axis1" name="x_axis[0]" value="x">
               <label for="x_axis1">x</label>
            </div>
            <div>
               <input type="checkbox" id="y_axis1" name="y_axis[0]" value="y">
               <label for="y_axis1">y</label>
            </div>
         </div>
    </div>
    <div class="box-wt200">
       <select multiple="multiple" id="mul_sel_v2" name="variables[1][]" placeholder="Variable 2" class="multi-select form-control dropdown-variable">
       </select>//I want to send these values via ajax call
       <div class="xyd-inline">
          <div>
             <input type="checkbox" id="x_axis2" name="x_axis[1]" value="x">
             <label for="x_axis2">x</label>
          </div>
          <div>
             <input type="checkbox" id="y_axis2" name="y_axis[1]" value="y">
             <label for="y_axis2">y</label>
          </div>
       </div>
    </div>
</div>

$selections = $this->input->post('selections');
$x_axis = $this->input->post('x_axis');
$y_axis = $this->input->post('y_axis');