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From: awu on 27 Jul 2010 07:30
Dear all,

Is there someone know that MatLab can work on surface area calculation or cannot?
I have 3-D surface of fuction z = sin(x)cos(y)+sin(3x)cos(3y)/9.
I need to know the surface area above a certain x-y region.
How can I get the surface integral from MatLab?

--
Thanks
From: us on 27 Jul 2010 07:39
"awu " <arwut365(a)hotmail.com> wrote in message <i2mg0f$mtj$1(a)fred.mathworks.com>...
> Dear all,
>
> Is there someone know that MatLab can work on surface area calculation or cannot?
> I have 3-D surface of fuction z = sin(x)cos(y)+sin(3x)cos(3y)/9.
> I need to know the surface area above a certain x-y region.
> How can I get the surface integral from MatLab?
>
> --
> Thanks

a hint:

help dblquad; % <- and siblings...

us
From: awu on 27 Jul 2010 09:14
"us " <us(a)neurol.unizh.ch> wrote in message <i2mggo$pic$1(a)fred.mathworks.com>...
> "awu " <arwut365(a)hotmail.com> wrote in message <i2mg0f$mtj$1(a)fred.mathworks.com>...
> > Dear all,
> >
> > Is there someone know that MatLab can work on surface area calculation or cannot?
> > I have 3-D surface of fuction z = sin(x)cos(y)+sin(3x)cos(3y)/9.
> > I need to know the surface area above a certain x-y region.
> > How can I get the surface integral from MatLab?
> >
> > --
> > Thanks
>
> a hint:
>
> help dblquad; % <- and siblings...
>
> us

It maybe different that the solution is a volume under the surface not surface area.
For example
Q = dblquad(@(x,y)3*x, 0, 2, 0, 2) gives-->Q=12
It looks like the volume of triangular prism (base is 2X2 and height=6).
The surface area that I need should be only top face of the prism (=2 X sqrt(2^2+6^2)).


-awu
From: Torsten Hennig on 27 Jul 2010 05:43
> "us " <us(a)neurol.unizh.ch> wrote in message
> <i2mggo$pic$1(a)fred.mathworks.com>...
> > "awu " <arwut365(a)hotmail.com> wrote in message
> <i2mg0f$mtj$1(a)fred.mathworks.com>...
> > > Dear all,
> > >
> > > Is there someone know that MatLab can work on
> surface area calculation or cannot?
> > > I have 3-D surface of fuction z =
> sin(x)cos(y)+sin(3x)cos(3y)/9.
> > > I need to know the surface area above a certain
> x-y region.
> > > How can I get the surface integral from MatLab?
> > >
> > > --
> > > Thanks
> >
> > a hint:
> >
> > help dblquad; % <- and siblings...
> >
> > us
>
> It maybe different that the solution is a volume
> under the surface not surface area.
> For example
> Q = dblquad(@(x,y)3*x, 0, 2, 0, 2)
> gives-->Q=12
> It looks like the volume of triangular prism (base is
> 2X2 and height=6).
> The surface area that I need should be only top face
> of the prism (=2 X sqrt(2^2+6^2)).
>
>
> -awu

Given a surface in the form
z=f(x,y),
the area of the surface area over a region D is
given by
int_{D} sqrt((dz/dx)^2+(dz(dy)^2+1) dA.
So
dz/dx = cos(x)*cos(y)+1/3*cos(3x)*cos(3y)
dz/dy = -sin(x)*sin(y)-1/3*sin(3x)*sin(3y)
...
Plug in and call dblquad with the appropriate function.

Best wishes
Torsten.
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