Using a vector input in integral function.

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fizzy
fizzy 2020-7-30
评论： fizzy 2020-7-31
Let's say I have a function "myfun" of variable x and its integral:
myfun = @(x) x; % A continuous function of variable x (exist for any x value between integration limit, 1 to 5)
myfunint = integral(myfun,1,5); % integration between x=1 and x=5
Now I have a vector which is also a function of this same variable x (but it's a vector!)
myvec= [0.5 1.5 2.5 3.5 4.5]; % values corresponding to x = 1,2,3,4,5
and my new function "myfunnew" is a multiplication of myvec with myfun..something like
myfunNew = @(x) myvec(x).*x; % Not continuous because myvec(x) only exists for certain x values (x=1,2,3...5) and not for values inbetween.
myfunNewint = integral(myfunNew,1,5)
and I want to use integral function on myfunNew.
But it won't work because "myvec" is a vector and "myvec(x)" doesn't exist for a lot of values of x between 1 and 5 that may be required by integral function when it evaluates integral. So my question is:
  • How can I convert this vector "myvec" to a continuous function (preferably using linear interpolation for missing values) so that I can use it in "myfunNew" such that it becomes integrable.
I can not use trapz.
  2 个评论
fizzy
fizzy 2020-7-30
Because that's not what I need. The result of integration, myfunNewint, will be a single value.

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采纳的回答

Alan Stevens
Alan Stevens 2020-7-31
Like this?
X = 1:5;
myvec= [0.5 1.5 2.5 3.5 4.5]; % values corresponding to x = 1,2,3,4,5
vec =@(x) interp1(X,myvec,x); % linear interpolation
myfunNew = @(x) vec(x).*x;
myfunNewint = integral(myfunNew,1,5)
  1 个评论
fizzy
fizzy 2020-7-31
Exactly! This is so simple. I guess I wasn't using the correct words in google search

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