docs: public double[][] getCovmat() {
      // Since we worked only on params with dofit=true, we need to expand the
      // matrix to cover all parameters.
      double[][] fullcov = new double[numparams][numparams];
      for(int i = 0, i2 = 0; i < numparams; i++) {
        for(int j = 0, j2 = 0; j < numparams; j++) {
          fullcov[i][j] = (dofit[i] && dofit[j]) ? covmat[i2][j2] : 0;
          if(dofit[j]) {
            j2++;
          }
        }
        if(dofit[i]) {
          i2++;
        }
      }
      return fullcov;
    }