Subject: Substituting a value for a differential function
From: Stavros Macrakis
Date: Tue, 27 Mar 2012 14:35:04 -0400
In general, in Maxima it is easier and more natural to work with
expressions (which you can assign to variables) than with explicitly
defined functions. Thus:
C: A*t^2+B*t+C;
dC: diff(C,t);
subst(t=25,dC);
-s
On Tue, Mar 27, 2012 at 11:46, Jaime Villate <villate at fe.up.pt> wrote:
> On 03/27/2012 04:33 PM, Vishnu Rajasekharan wrote:
>
>> I have a function below. I am trying to subsitute t=25 in the dC(t) and
>> I am getting an error. Please let me know what I missing ot get the value
>> of the differential function.
>> C(t):=(Ax^2)+(Bx)+C
>> dC(t):=(diff(C(t),t,1))$
>>
> Hi,
> there are several things that you must have in mind here:
>
> 1) I think you meant A*x^2 and B*x instead of Ax^2 and Bx.
> 2) I think you meant t instead of x in the definition of C(t).
> 3) The operator := does not calculate the right side before defining the
> function. That means
> that when you try to replace t=15, that substitution will be made before
> the function is differentiated.
>
> Try it this way:
>
> (%i2) define (C(t), A*t^2+ B*t+C);
>
> (%o2) C(t):=C+t*B+t^2*A
> (%i3) define (dC(t), diff(C(t),t));
>
> (%o3) dC(t):=B+2*t*A
> (%i4) dC(15);
>
> (%o4) B+30*A
>
> define(f(x), exp) is similar to :=, but the exp will be simplified before
> f(x) is defined. In some cases
> one needs := and in some other cases define().
>
> Cheers,
> Jaime
>
> ______________________________**_________________
> Maxima mailing list
> Maxima at math.utexas.edu
> http://www.math.utexas.edu/**mailman/listinfo/maxima<http://www.math.utexas.edu/mailman/listinfo/maxima>;
>