Calculate the area between two curves

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maria
maria 2014-4-10
编辑： Alberto 2014-4-11
i need help! i am new at using the Matlab and Scilab softwares and i need to calculate the area between the curves y=f(x) and y=g(x) in the interval [a,b] with a = 3, b = 6,
f (x)=sin(3 x+1) and g(x)=(e∣x∣/2−2−1)
by means of the composite trapezoidal rule with 73 trapezoids,Recall that the area between f and g in [a,b] is
b a ∫ ∣f(x)−g(x)∣dx
The approximate value of the area has to be displayed at the end, and the script must contain all the code to obtain the result.
how do i even begin with this? any help is much appreciated. thanks

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Alberto
Alberto 2014-4-11
f =@(x) sin(3.*x+1) ;
g=@(x) exp(abs(x)/2 -2)-1;
a=3; b=6;
x=linspace(a,b,73); S=0;
for k=1:length(x)-1
S=S+abs( f(x(k+1)) - g(x(k+1)) - f(x(k)) +g(x(k)) )/2;
end
S
  2 个评论
maria
maria 2014-4-11
thank you! thank you!!! i have tried this out on my pc.. and i get S = 0 for all 72 columns. is this it for that question or is there another step afterwards and i have uploaded an image that came with the question. please take a look at it.. i know i am hopeless but bear with me for a bit longer..
Alberto
Alberto 2014-4-11
编辑：Alberto 2014-4-11
Actually S is not a vector; S has the cumulative sum of trapezoids. The value I get is:
S = 2.7752
and has no columns. Maybe there are some conflicts with other parts.
Show me your whole code so I can check

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