title: Force a LM coefficient to a value
body: <p>I am working on a project about weights for Screws.</p>
  
  <p>I looped through and found the fits for a number of combinations like shown below.</p>
  
  <pre><code>head style       measurement  intercept     slope
  a                1            x             1.0
  a                2            x             2.2
  a                3            x             4.1
  b                1            x             1.2
  b                2            x             2.0
  b                3            x             4.1
  </code></pre>
  
  <p>If I know for a fact that the ones with the same measurement should have the same slope.  So a-1 should have the same slope as b-1.  Is there a way I could run another lm where I set the slopes to be a set number?</p>