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Solve or NSolve doesn't give any solution in twelve hours

Posted 10 years ago
I typed 

NSolve[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/
    2673) <= 50, t]

with an equality (50) or inequality (<=50), with Solve or NSolve, and wihin 12 hours I don't get a solution.

What is wrong ?
POSTED BY: bilik.miloslav
3 Replies
Posted 10 years ago
Many thanks, adding "Reals" solves the problem. I don't know Reduce or FindInstance and I will look, thx again for your hints.
POSTED BY: bilik.miloslav
NSolve[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/2673) == 50, t, Reals]
(*{{t -> 0.1402163037}, {t -> 143.2657137}}*)
Took about 40 seconds on my PC.

For inequality, one is supposed to use Reduce[]. But it was taking long time on my end. You can also use FindInstance if you just want one solution:
FindInstance[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/2673) <= 50, t]
(* {{t -> 0}} *)
POSTED BY: Nasser M. Abbasi
FindRoot[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/
     2673) == 50, {t, 1}]
{t -> 0.140216}
returns almost immediately.  Since there are mulitple solutions, the one that you get will depend on the starting value you give to FindRoot.
POSTED BY: Frank Kampas
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