title: Inequality constraints in systemfit
body: <p>I'm trying to estimate a simultaneous equations system using <code>systemfit</code>, but cannot seem to specify inequalities as constraints. I've recreated the problem using the <code>airquality</code> dataset, the issue arises when adding inequalities to the <code>restrict.matrix</code> argument. Is there any workaround to get this example to work?</p>
  
  <pre><code>require(systemfit)
  
  lagAQ &lt;- rbind(NA, airquality[1:nrow(airquality)-1,])
  colnames(lagAQ) &lt;- paste("lag", colnames(lagAQ), sep = "")
  data &lt;- data.frame(airquality, lagAQ)
  
  eqOzone &lt;- Ozone ~ lagOzone + lagWind + lagTemp
  eqWind  &lt;- Wind ~ lagOzone + lagWind + lagTemp
  eqTemp  &lt;- Temp ~ lagOzone + lagWind + lagTemp
  
  airSystem &lt;- list(ozone = eqOzone, wind = eqWind, temp = eqTemp)
  
  constr &lt;- c("ozone_(Intercept) = 0",
              "wind_(Intercept) = 0",
              "temp_(Intercept) = 0",
  
              "ozone_lagOzone &gt; 0",
              "ozone_lagWind &gt; 0",
              "ozone_lagTemp &gt; 0",
  
              "ozone_lagOzone + wind_lagOzone + temp_lagOzone = 1",
              "ozone_lagWind + wind_lagWind + temp_lagWind = 1",
              "ozone_lagTemp + wind_lagTemp + temp_lagTemp = 1"
              )
  
  airModel &lt;- systemfit(airSystem, restrict.matrix = constr, data = data)
  </code></pre>