# What implementation does sage use for solve?

What algorithm does sage use when you solve polynomials with the solve() function?

What implementation does sage use for solve?

**
asked 2021-04-19 20:48:21 +0200 **

Anonymous

What algorithm does sage use when you solve polynomials with the solve() function?

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Regarding the `solve`

function, Sage does not implement it own algorithm, instead it asks `maxima`

to do the job by default. You can also pass the `algorithm='sympy'`

option to use Sympy instead.

See:

```
sage: solve?
```

What algorithm does maxima use then? There are numerious methods to solve polynomials like Durand-Kerner...

We have to check. Note however that the Durand-Kerner algorithm is numerical, while the `solve`

function will try to give you the solutions as symbolic expressions involving nth roots:

```
sage: solve(2*x^2-7==0,x)
[x == -1/2*sqrt(7)*sqrt(2), x == 1/2*sqrt(7)*sqrt(2)]
```

So is it safe to say that say that Sage solves polynomials analytically instead of numerically? Do you know how they implement such algorithm? You would think that a computer solves factorization nummerically since it can easilly calculate a lot of numbers with decent precision.

So is it safe to say that say that Sage solves polynomials analytically instead of numerically?

Yep, when possible. When not possible (degree >=5, and no "obvious" paths to an explicit solution, Sage can compute root values in QQbar, which can be thought of as objects representing *algorithms*, computable to *arbitrary* precision and are treated as *exact* numbers by "the rest of Sage".

Do you know how they implement such algorithm?

Tou are welcome to read the source ;-) (translation : I don't know, do not know enough to know where to start...).

You would think that a computer solves factorization numerically since it can easily calculate a lot of numbers with decent precision.

That's more or less what happens when an explicit solution (first intention goal) does not exist.

You could also ask on the Maxima mailing lists: https://maxima.sourceforge.io/maximal...

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Asked: ** 2021-04-19 20:48:21 +0200 **

Seen: **266 times**

Last updated: **Apr 19 '21**

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