how to make maxima create equation like i give in attachment

Sorry for the bug in atvalue.

You can replace the f[i,j]'s with the atomic f_i_j using subst(
concat("f_",i,"_",j), f[i,j], ... ).  Or even easier, define:

     f[n,k] := concat("f_",n,"_",k)

and then whenever you write f[n,k], it will evaluate to f_n_k.

You also need to either declare all the f_n_k's as depending on s or,
better, write 'diff(...) instead of diff(...).

            -s

On Thu, Jan 13, 2011 at 03:44, razif razali <razif66 at gmail.com> wrote:

> Macrakis,
>
> Here example that I used 'desolve' for my problem,
> --------------------------------------------------------------------
> eq1:diff(f(s),s)=-sqrt(2)*g(s)*k;
>
> eq2:diff(g(s),s)=k*(sqrt(2)*f(s)-2*h(s));
>
> eq3:diff(h(s),s)=2*k*g(s);
>
> atvalue(f(s),s=0,f0);
>
> atvalue(g(s),s=0,0);
>
> atvalue(h(s),s=0,0);
>
> desolve([eq1,eq2,eq3],[f(s),g(s),h(s)]);
>
> nonzero;
> ---------------------------------------------------
>
> I manually replace f[4,1] to f(s), f[4,2] to g(s) and f[4,3] to h(s)
> because 'atvalue' can't accept f[4,1](s), it will give error.
>
> so how to make maxima automatically convert all those f[n,k] function into
> f(s),g(s),h(s).....n(s) in code below so that I can used code above to solve
> my problem?
>
> --------------------------------------
> depends(f,s);
> df[n,k] :=
>   if n=0
>     then 0
>   else
>
> diff(f[2*n,k],s)=x*((k-1)*sqrt(n-k+2)*f[2*n,k-1]-k*sqrt(n-k+1)*f[2*n,k+1]);
> eqs:makelist(df[2,k],k,1,3);
> -----------------------------------------
>
> or maybe there some way that we didn't need to replace the function but
> make maxima solve it automatically?
>
> On Thu, Jan 13, 2011 at 12:41 PM, Stavros Macrakis <macrakis at alum.mit.edu>wrote:
>
>> Razif,
>>
>> In Maxima, you do not assign values to derivatives etc.  You write
>> equations and can store the equations in variables or lists.
>>
>> Let me give an example with ordinary (not differential) equations.
>>
>> eq1:  x = y+3$
>> eq2:  x*5=2*y-7$
>>
>> solve( [eq1, eq2], [x,y]);
>>
>> OR
>>
>> eqs: [ x = y+3,  x*5=2*y-7 ]$
>> vars: [x,y]$
>> solve(eqs,vars);
>>
>> You can do the same thing for systems of equations using 'makelist':
>>
>> eqs: makelist( x[ i ] = x[ i+1 ] + x[ i-1 ] + 1, i , 1, 5 )$
>>  solve(    append([x[0]=x[8],x[3]=1],eqs),      << add some extra
>> equations
>>              makelist(x[i],i,0,8));                       << list of
>> variables
>>
>> I have not worked with the differential equation solvers for a long time,
>> so I don't know whether they can solve your equations.
>>
>>            -s
>>
>>
>>
>>
>> On Wed, Jan 12, 2011 at 22:46, razif razali <razif66 at gmail.com> wrote:
>>
>>>
>>>
>>> On Thu, Jan 6, 2011 at 9:40 PM, Leo Butler <l.butler at ed.ac.uk> wrote:
>>>
>>>>
>>>>
>>>> On Thu, 6 Jan 2011, razif razali wrote:
>>>>
>>>> < Thanks for your reply,
>>>> < so from your guide, here what I come through,
>>>> < ------------------
>>>> < df(n,k):=
>>>> < block ([],
>>>> <     if n=0
>>>> <     then 0
>>>> <   else
>>>> <
>>>>   'diff(f[2*n,k],s)=x*((k-1)*sqrt(n-k+2)*f[2*n,k-1]-k*sqrt(n-k+1)*f[2*n,k+1])
>>>> < );
>>>> < makelist(df(1,k),k,1,2);
>>>> < ------------------------
>>>> < I can get the equation for diff( f[2,1],s) and diff( f[2,2],s)
>>>> respectively,
>>>> <
>>>> < so next thing is, how can i make diff( f[2,1],s) and diff( f[2,2])
>>>> hold it value?because when I type again diff( f[2,1],s) in maxima after give
>>>> code above, it gives
>>>> < zero. what i want do here is after i get equation diff( f[2,1],s) i
>>>> want to solve with both equation using ode method to get function of f[2,1]
>>>> and f[2,2] with
>>>> < f[2*n,k](0)=A, and value of x and A are not zero...
>>>>
>>>>  The problem is that Maxima does not know that f[n,k] is a function of
>>>>  s, too. Here is a solution:
>>>>
>>>>  depends(f,s);
>>>>  df[n,k] := if n=0 then 0 else
>>>> diff(f[2*n,k],s)=x*((k-1)*sqrt(n-k+2)*f[2*n,k-1]-k*sqrt(n-k+1)*f[2*n,k+1]);
>>>>  .
>>>>  .
>>>>  .
>>>>  Note that I do not use 'diff, because the first line tells Maxima
>>>>  that f is a function of s.
>>>>
>>>> Leo
>>>> --
>>>> The University of Edinburgh is a charitable body, registered in
>>>> Scotland, with registration number SC005336.
>>>>
>>>> by telling MAXIMA that f[n,k] is function of s to helped me without
>>> using 'diff but then it still not hold the function for next used?
>>> the result still the same,
>>>
>>> depends(f,s);
>>>  df[n,k] := if n=0 then 0 else
>>> diff(f[2*n,k],s)=x*((k-1)*sqrt(n-k+2)*f[2*n,k-1]-k*sqrt(n-k+1)*f[2*n,k+1]);
>>> makelist(df[1,k],k,1,2);
>>>
>>> then i got the diff(f [2,1],s) and diff( f[2,2],s)
>>>
>>> so how to make diff(f [2,1],s) and diff( f[2,2],s) hold its function so
>>> that I can solve it using ODE in MAXIMA?because when i type all command
>>> above and get the result, when i type again diff( f[2,1],s) it give
>>> nothing...
>>>
>>>
>>>
>>>
>>> --
>>> Regards,
>>>
>>> RAZIF RAZALI,
>>> Tutor & Master Student,
>>> Physics Department,
>>> Faculty Of Science,
>>> Universiti Teknologi Malaysia(UTM).
>>> +60199393606
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Maxima mailing list
>>> Maxima at math.utexas.edu
>>> http://www.math.utexas.edu/mailman/listinfo/maxima
>>>
>>>
>>
>
>
> --
> Regards,
>
> RAZIF RAZALI,
> Tutor & Master Student,
> Physics Department,
> Faculty Of Science,
> Universiti Teknologi Malaysia(UTM).
> +60199393606
>
>
>
>