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MATlab #help

Anonymous Wed 25 Sep 2019 07:45:12 No.718785 View View Reply Original Report

Quoted By:

help me do matlab please.
Its the trapozoid Method, pic related is the task, i'll reply With the function and a pic of my matlab. thanks in advance!

Anonymous

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Anonymous Wed 25 Sep 2019 07:49:35 No.718787 Report

Quoted By:

here is what i've written. The res expression is my f(x), don't know how to rewrite it to f(x) to be honest.

Anonymous

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Anonymous Wed 25 Sep 2019 07:50:46 No.718789 Report

Quoted By:

Same anon, had to post it from different computer lol self bump

Anonymous

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Anonymous Wed 25 Sep 2019 08:17:19 No.718799 Report

Quoted By: >>718802

updated it now, the answer i get is -0.016, which can't be right??

Anonymous

Anonymous Wed 25 Sep 2019 08:22:23 No.718800 Report

Quoted By: >>718801 >>718807 >>718809

your formula s not correct

10) step = (b-a)/n
s = f(a)/2 + f(b)/2

12) s = s + f(a + k* step)

14) s = s* step

Anonymous

Anonymous Wed 25 Sep 2019 08:25:04 No.718801 Report

Quoted By:

>>718800
thanks anon, ill try it out

Anonymous

Anonymous Wed 25 Sep 2019 08:26:16 No.718802 Report

Quoted By: >>718804

>>718799
12) 13) become s = gauss(a)/2 + gauss(b)/2
16) s = s + gauss(a+k*h);
18) I = h*s;

Anonymous

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Anonymous Wed 25 Sep 2019 08:31:15 No.718804 Report

Quoted By:

>>718802
doing this, i end up with answer
answer=-0.996531>>

Anonymous

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Anonymous Wed 25 Sep 2019 08:33:29 No.718807 Report

Quoted By: >>718809

>>718800
f is not defined, therefore i get error when doing this. I use the function gauss(x), which is a function i defined in an earlier task

Anonymous

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Anonymous Wed 25 Sep 2019 08:35:12 No.718809 Report

Quoted By: >>718845

>>718807
>>718800
Also, the answer becomes the same as before, -0.016, which i don't know if is correct

Anonymous

Anonymous Wed 25 Sep 2019 11:23:58 No.718845 Report

Quoted By:

>>718809
>step = (b-a)/n
>s = f(a)/2 + f(b)/2
before for

> s = s* step
after end of for

and he solution should be ~ 1

Anonymous

Anonymous Wed 25 Sep 2019 13:00:35 No.718861 Report

Quoted By: >>718863

Your mistake is that you are not saving the result between cycle steps.
I would do it simply:
>ks = 1:n-1
>as = ones(1, n-1) * a
>coef = (b-a)/2
>result = coef * (f(a)/2 + sum(arrayfun(@f, as + ks*coef) + f(b)/2)
If the function can be applied on whole array/matrix at once, you don't have to use arrayfun, you could change last line to:
>result = coef * (f(a)/2 + sum(f(as + ks*coef)) + f(b)/2)

Using "for" is inferior solution, but if you want, I can post it too.

Anonymous

Anonymous Wed 25 Sep 2019 13:05:10 No.718863 Report

Quoted By:

>>718861
My matlab is rusty, shows that I didn't touch it for years, you don't have to have as variable, you can do simply:
>ks = 1:n-1
>coef = (b-a)/2
>result = coef * (f(a)/2 + sum(arrayfun(@f, a + ks*coef) + f(b)/2)
or
>result = coef * (f(a)/2 + sum(f(a + ks*coef)) + f(b)/2)

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