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# how can I do Iteration in matlab

Asked by Ede gerlderlands on 17 Nov 2012

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.

## Products

Answer by Azzi Abdelmalek on 17 Nov 2012
Edited by Azzi Abdelmalek on 17 Nov 2012

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)```

## 1 Comment

Ede gerlderlands on 17 Nov 2012

Many many thanks ...don't have words for your help....this was so troublesome...

Answer by Azzi Abdelmalek on 17 Nov 2012
Edited by Azzi Abdelmalek on 17 Nov 2012

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)
```

Ede gerlderlands on 17 Nov 2012

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 on 17 Nov 2012

Thanks Azziz , I understand your function but 'a' itself isn't known and that's my problem.

Azzi Abdelmalek on 17 Nov 2012

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.