Confused by Integration

[Jason C. Wells]

I am confused by integration.  I see that the various quad function take 
different types (scalar, vector) and give different outputs.  I've been 
trying them out and watching how the quadrature behaves for each of 
them. E.g:

        function retval = integrand (x)
            x
            retval = x .^ 2
        endfunction

        # integral = quadv ("integrand", -Inf, Inf)

        a = -10: 1: 10;
        integral = quadgk ("integrand", a(1), a(end))

Quadgk seems close to what I want, but the variable of integration 
"bounces around" which makes plotting impossible.

x=
      -9.999989
      -9.435377
      -7.911791
      -5.669229
      -2.947694
       0.012817
       2.972302
       5.690762
       7.928196

Ultimately I'd like to make a plot of the integral.  It seems that all 
of the quadrature functions do not pay attention to the the range i've 
given.  The functions do their own thing within the limits of integration.

Does a person need to run the integration, then re-sort and 
re-interpolate in order to produce outputs at evenly spaced inputs?

How do I integrate such that each output value corresponds with an input 
value taken from a range of from a linspace vector?

Thanks in advance,
Jason C. Wells