title: How to make an expression from model fixed effects?
body: <p>I have the fixed effects from lmer in an object, fixed.effects3, and I want to make an expression that I can use as a formula for plotting with curve(). I tried this:</p>
  
  <pre><code>math.growth &lt;- expression(eval(fixed.effects3[1]) + x*eval(fixed.effects3[2]) + x^2*eval(fixed.effects3[3]))
  </code></pre>
  
  <p>but then when I try to plot it with curve() I get these errors:</p>
  
  <pre><code>curve(math.growth, from=-2, to=3)
  Error in eval(expr, envir, enclos) : 
  could not find function "math.growth"
  </code></pre>
  
  <p>Can someone tell me what I'm doing wrong?</p>