Le 11/05/2010 23:06, Chris Maness a ?crit :
> I am having trouble finding a numeric solution to this equation:
>
> solve(P*(.001+(2.54e-4)*(2/1000*P)^(1/2)*t)^(7/5)=43.5,P);
>
> It works when t:0;
>
> but when I plug in different values for t, it does not seem to be able
> to find a solution.
>
> Is there some kind of numeric method (like Newton's method) that can solve this?
>
>
Yes, a dichotomy using find_root is possible since your function is
increasing and continuous :
f(P,t):=P*(.001+(2.54*10^-4)*(2/1000*P)^(1/2)*t)^(7/5)-43.5;
find_root(f(P,5.7),0,100000); ------------------>
23953.99528067121
You can also use Newton's method, first loading the package newton1 :
load (newton1);
newton(float(f(x,5.7)),x,20000,1/1000); ------------------>
23953.99529030703
Note the float, otherwise f is evaluated symbolically ( huge garbage on
the screen !).
You can find the word newton in the index of the online help. Then
browse around, there is a link to numerical methods giving the find_root
function.
Eric
> Regards,
> Chris Maness
> _______________________________________________
> Maxima mailing list
> Maxima at math.utexas.edu
> http://www.math.utexas.edu/mailman/listinfo/maxima
>
>