title: Setting custom Alpha in pandas EWM function
body: <p>I'm trying to smooth the closing price with a customer alpha but it does not seem to work. I receive the following message below</p>
  
  <pre><code>raise ValueError("comass, span, halflife, and alpha "
  ValueError: comass, span, halflife, and alpha are mutually exclusive
  </code></pre>
  
  <p>this is the code I am running</p>
  
  <pre><code>import warnings
  warnings.filterwarnings('ignore')
  
  import pandas_datareader.data as webb
  
  df = web.DataReader('AAPL', 'yahoo', '2020-01-01', '2019-12-31')
  df.reset_index(inplace=True)
  
  df['ema'] = df['Close'].ewm(span=10, alpha=3.0,adjust=True).mean()
  </code></pre>
  
  <p>I tried researching the issue but could not find much on the topic</p>
  
  <p>Thanks</p>