On Feb 10, 5:38 am, Thomas Scofield <[email protected]> wrote:
> I borrowed/adapted the following code for carrying out a line integral  
> from a published notebook
>
>     var('x,y,t')
>     F=vector([x^2,x*y])
>     r=vector([cos(t), sin(t)])
>     tstart=0
>     tend=2*pi
>     integrand = F(x=r[0], y=r[1])*diff(r,t)
>
> As one may observe, integrand is identically 0.  The idea is now to  
> carry out the command
>
>     numerical_integral(integrand, tstart, tend)

integrand is an *expression* after you are done. numerical_integration
needs a function in one variable. Apparently, the routine is
permissive and also accepts expressions that it can easily interpret
as a function in one variable. However, the constant 0 apparently
doesn't fall in that category. You can be explicit and tell the system
to regard integrand as a function in t::

numerical_integral(integrand.function(t), 0, 1)

works.

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