how can I do Iteration in matlab

2012 11 17
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I have an equation of the form
a(x) + x.da/dx = 2x , x= 1:1:12
f(x) is known and has different values for different x. My question is how can I find values of 'a' in matlab through iteration. Am new to matlab and any help is highly appreciated.

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Azzi Abdelmalek
Azzi Abdelmalek 2012-11-17
编辑：Azzi Abdelmalek 2012-11-17

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save this function with the name dif_eq
function da=dif_eq(x,a,tim,f)
f1=interp1(tim,f,x)
da=(f1-a)/x;
then call the function:
t=[0.1:10]; % time vector
x0=0; % initial condition
f=rand(1,numel(t)); % your vector f, same length as vector time t
[X,A]=ode45(@(x,a) dif_eq(x,a,t,f),t,x0);
plot(X,A)

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Ede gerlderlands
Ede gerlderlands 2012-11-17
Many many thanks ...don't have words for your help....this was so troublesome...

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Azzi Abdelmalek
Azzi Abdelmalek 2012-11-17
编辑：Azzi Abdelmalek 2012-11-17

0 个投票

save this funnction with the name dif_eq
function da=dif_eq(x,a)
f=sin(x); for example
da=(f-a)/x;
then type in Matlab command
[x,res]=ode45(@dif_eq,[1 12],0)

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Ede gerlderlands
Ede gerlderlands 2012-11-17
Thanks Azzizi can you clarify me how can I insert the 'f' value in my command and the second is this equation can solve the differential part of the equation. My equation is a(x) + x.da/dx = f(x),
Azzi Abdelmalek
Azzi Abdelmalek 2012-11-17
编辑：Azzi Abdelmalek 2012-11-17
You said that f is a function of x, then replace in my code, f=sin(x) by your own function
The code I did solves your differential equation
Ede gerlderlands
Ede gerlderlands 2012-11-17
Yes, I did that my actual 'f' is not function actually it is collection of different values. such as 0.4 0.25 0.6.....
Ede gerlderlands
Ede gerlderlands 2012-11-17
Thanks Azziz , I understand your function but 'a' itself isn't known and that's my problem.
Azzi Abdelmalek
Azzi Abdelmalek 2012-11-17
Ede, the problem is not a, we are looking for a. I can't use f with different values in the equation. If I find something I will post it, or someone else will do.

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