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From: Michelle on 18 Jan 2010 17:11
Hi,

I'm trying to create a function m-file that will compute the work required to pump all the water out and up to a point which is distance a above the top of a point-down conical tank with radius r and height h. The function takes r, h, and a as it's three arguments. I'm using quad for the integral.
I need to use the m-file to evaluate a tank with r=7, h=2, and an unknown a, but matlab just keeps telling me that a is undefined. I know that the if I integrate with respect to the right variable the integral should be able to handle 'a' being an uknown constant, but I can't figure out how to do that.
Here's the m-file I have right now:

function t=fuckmylife15(r,h,a)
syms x;
t=62.5 * quad(@(x) pi .* r .^2 .* ((h+a)-x), 0, h+a)

Any help would be greatly appreciated. Thanks.
From: Michelle on 18 Jan 2010 17:19
Whooooops, probably should have changed that function name before posting it here. Sorry.
From: Michelle on 18 Jan 2010 18:06
And I fixed my integral:
62.5 * quad(@(x) pi .* ((r./h).* x) .^2 .* ((h+a)-x), 0, h+a)
From: John D'Errico on 18 Jan 2010 18:10
"Michelle " <captainofthestarshipenterprise(a)hotmail.com> wrote in message <hj2m9o$lsl$1(a)fred.mathworks.com>...
> Hi,
>
> I'm trying to create a function m-file that will compute the work required to pump all the water out and up to a point which is distance a above the top of a point-down conical tank with radius r and height h. The function takes r, h, and a as it's three arguments. I'm using quad for the integral.
> I need to use the m-file to evaluate a tank with r=7, h=2, and an unknown a, but matlab just keeps telling me that a is undefined. I know that the if I integrate with respect to the right variable the integral should be able to handle 'a' being an uknown constant, but I can't figure out how to do that.
> Here's the m-file I have right now:
>
> function t=integrate_this(r,h,a)
> syms x;
> t=62.5 * quad(@(x) pi .* r .^2 .* ((h+a)-x), 0, h+a)
>
> Any help would be greatly appreciated. Thanks.

You apparently wish to integrate this as a
function of a, where a is left symbolic. The
flaw in your plan is that quad is a NUMERICAL
integration tool. It cannot integrate a symbolic
integrand. For that, you need to use the
integration facility of the symbolic toolbox.

John
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