You probably want to define an expression
functionbody: phi1(xi)*V1*diff(phi1(xi)*A(xi,t),xi);
which evaluates the derivative, puts in the body of phi1 and A() etc.
and then
Ai11(xi):=''functionbody;
{that's two ' marks there.)
At least that's my guess, after looking at this for 60 seconds.
There are more complicated ways of doing the same thing.
RJF
Angus Leeming wrote:
> On Wednesday 11 May 2005 15:55, Viktor T. Toth wrote:
>
>>Your legendre_root function, used in
>>
>> x : legendre_root(order,i),
>>
>>returns a number, e.g.:
>>
>>(%i46) legendre_root(4,0);
>> sqrt(15 - 2 sqrt(30))
>>(%o46) - ---------------------
>> sqrt(35)
>>
>>This number is then supplied as the function argument xi:
>>
>> sum : sum + (w * func(x))),
>>
>>to your anonymous (lambda) function. The function then calls diff() with
>>xi as its second argument, i.e., it tries to differentiate with respect
>>to a number, as opposed to a variable:
>
>
> Yes, I understand. I guess I was asking how should I go about writing this
> thing 'correctly'?
>
> Can I call func so that it performs the analytic differentiation and then
> substitute for values of x?
>
>
>>quad(order,func):=
>> block([sum, x, w],
>> sum:0,
>> for i:0 thru order-1 do (
>> x : legendre_root(order,i),
>> w : gauss_legendre_weight(order,i),
>> sum : sum + (w * func(x))),
>> return(sum)
>> )$
>
>
> Angus
>
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