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Topic: integral that includes symbols
Replies: 4   Last Post: Aug 6, 2013 1:50 PM

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Young Ryu

Posts: 138
Registered: 1/7/08
Re: integral that includes symbols
Posted: Aug 6, 2013 10:05 AM
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"Torsten" wrote in message <ktqpcf$ga0$1@newscl01ah.mathworks.com>...
> "Young " <ryuyr77@gmail.com> wrote in message <ktql9j$6n2$1@newscl01ah.mathworks.com>...
> > Hi
> >
> > I have an equation: F=L*cos(theL). L is a constant. Integral of F over zero to (1/2)pi should give L. But I could not make that answer Please see below my code and help me how to fix this problem. I have much more complex equation but simplified my problem to this example.
> >
> > syms L;
> > theL=[0+0.001:pi/1000:pi/2-0.001]
> > F=L*cos(theL);
> > trapz(theL,F)
> >
> > ans: (21828504695225120901251714223243*L)/162259276829213363391578010288128 + (634496096455597832693*pi*L)/2305843009213693952000

>
> If you know the explicit formula for the function you want to integrate, then
> for symbolic integration use MATLAB's "int", for numerical integration use MATLAB's "quad".
>
> Best wishes
> Torsten.


Hi Torsten

Thanks for your help! But it did not work... Please see below. It looks "quad" does not allow to use sym... I need to use numerical solution.

-------------------------------------------------------------------------------------
syms L;
y=@(theL) (L*cos(theL));
quad(y,0,1/2*pi)

ans:
Undefined function 'isfinite' for input arguments of type 'sym'.
Error in quad (line 79)
if ~isfinite(y(1))



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