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Topic: calculate the area of a curve
Replies: 9   Last Post: Mar 24, 2013 8:53 AM

 Messages: [ Previous | Next ]
 dpb Posts: 9,850 Registered: 6/7/07
Re: calculate the area of a curve
Posted: Mar 23, 2013 2:22 PM

On 3/23/2013 1:02 PM, angelina wrote:
> "Nasser M. Abbasi" wrote in message <kikco2\$ops\$1@speranza.aioe.org>...
>> On 3/23/2013 7:57 AM, angelina wrote:
>> > Hi!
>> > I am not sure if there is a way to calculate the area of a curve in

>> matlab.
>>
>> curve does not have an area. it is just a curved line. it has a length
>> though
>> and it has curvature, but area?
>>

>> >What I want to do , is first , define the curve (which is a load
>> duration
>> >curve) and it is three piece linear.How can I define it?
>> > The coordinates are (0,100) , (2.8,75) and (100,25)
>> > Then , I want for the beginning to calculate the whole area af
>> >the curve and after that for many straight lines of the form y=a I want
>> >to calculate the area of the two areas that are created.
>> > Any comment or help woould be of great importance!
>> > Thanks a lot!
>> >

>>
>>
>> It sounds like you want to integrate a function and you have
>> only 3 points for it? May be you can look at trapz.
>>
>> http://www.mathworks.com/help/matlab/ref/trapz.html
>>
>> "Z = trapz(Y) computes an approximation of the integral of Y via the
>> trapezoidal method"
>>
>> good luck,
>>
>> --Nasser
>>

>
> Hi Nasser!
> It seems that I didn't explain correctly.
>
> What I want to do is this:
> I have that:
>
> X=[0 ; 0.028; 1;];
> Y=[1; 0.75; 0.25;];
> plot(X,Y);
> So if you plot this thing imagine that I want to find the area between
> the line and the axes x and y.After that for any line of the form y=g I
> want to find again the area between the line y=g y=-ax+, my initial line
> and the axes x and y .
> Thank you! I hope now I explained welll!
> I am waiting for any reply!
> Angelina

Well, for the line segments the area is analytically computable but
trapz() will work. Simply subtract the area of the lower curve(s) from
the upper.

--

Date Subject Author
3/23/13 Nasser Abbasi
3/23/13 dpb
3/23/13 Nasser Abbasi
3/23/13 dpb
3/24/13 Marc
3/24/13 dpb