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Error with Solve[] and floating-point coefficients

Hi, I want to ask you why When try to resolve a equation with inexact coefficients appear me this error

ERROR : Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result. >>

How can resolve it?

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POSTED BY: Giovanni Ferdina
4 Replies

Hi Giovanni,

it would be very useful if you could post the actual code, not just a screenshot. Here is a great post on, well, how to post: http://community.wolfram.com/groups/-/m/t/270507

It was quite difficult to read the screenshot, but I think that it all boils down to something like this:

Solve[6.34733 Sin[4.72654 x] - 0.546274 Sin[10.3090 x] == 0 && 0. < x < 10., x]

It appears that the equation has an infinite number of solutions,

enter image description here

so the additional constraint gives the roots in that interval. You still get the warning, but you do get results. When I typed exactly your equation in, I did not get a warning, but the calculation did not terminate within a couple of minutes. The warning just says that the coefficients are inexact numbers (Mathematica uses Machine Precision in your case), and that the algorithms behind Solve can only solve this with exact coefficients. Internally Mathematica converts everything and finds then solutions to the exact coefficients.

Cheers,

M.

POSTED BY: Marco Thiel

Thank you so much Mark, I thought Mathematica me back a root periodic interval instead need to find the root. Next time I will try to attach a screenshot of better quality Thanks again

POSTED BY: Giovanni Ferdina

Or even better: instead of attaching a screenshot you attach the actual code or use the formatting symbol to put the code directly into your post.

Cheers,

Marco

POSTED BY: Marco Thiel
DSolve[{k \!\(
\*SubscriptBox[\(\[PartialD]\), \(r\)]\((r\ 
\*SubscriptBox[\(\[PartialD]\), \(r\)]T[r])\)\) == 0, 
   T[a] == T0, -k T'[b] == qo} , T[r], r] // Simplify

Marco I do not understand, how do the formatting symbol to put the code Directly into my post? There is a menu in Mathematica where to click? With this response I try to press Code sample "Ctrl + k" in this space, and incorporate equation to prove.

POSTED BY: Giovanni Ferdina
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