possible bug in test_exp_pade and a fix

[Ondřej Čertík]

Hi Fredrik,

In this pull request:

https://github.com/sympy/sympy/pull/635

we have found a possible bug in mpmath, that Mario fixed with this patch:

https://github.com/pernici/sympy/commit/5745821120f01ff4638b5d87472649c307648800

Just see the pull request for background information. Do you think
that this patch should
be applied to mpmath upstream? It seems to fix the problem.

Ondrej

[Fredrik Johansson]

2011/10/11 Ondřej Čertík <ondrej...@gmail.com>:

Yes, it probably should.

Mario, can you commit this to the mpmath svn repository?

Fredrik

[mario]

Hi Fredrik,
I committed the same fix to mpmath which I put in sympy, but it does
not work.
I wanted to increase the precision in computing exp_pade; to do this I
wrote in calculus.py

```
if method == 'pade':
prec = ctx.prec
ctx.prec += 2*A.rows
A = ctx.matrix(A)
res = ctx._exp_pade(A)
```

and it works in sympy, but not in mpmath.
In fact putting e.g. `ctx.prec += 2*A.rows + 10` in mpmath nothing
changes, putting it in sympy it increases the
precision of norm(d,inf) in the test by 3 digits.
If in mpmath in the test I increase `mp.dps` by `3` before calling
`expm(a1, method='pade')` the precision of norm(d,inf) in the test
increases by 3 digits.
What am I doing wrong?

Mario

[Fredrik Johansson]

Hi Mario,

On Sun, Oct 30, 2011 at 1:07 PM, mario <mario....@gmail.com> wrote:
> Hi Fredrik,
> I committed the same fix to mpmath which I  put in sympy, but it does
> not work.

Thanks!

> I wanted to increase the precision in computing exp_pade; to do this I
> wrote in calculus.py
>
> ```
>        if method == 'pade':
>            prec = ctx.prec
>            ctx.prec += 2*A.rows
>            A = ctx.matrix(A)
>            res = ctx._exp_pade(A)
> ```
>
> and it works in sympy, but not in mpmath.
> In fact  putting e.g. `ctx.prec += 2*A.rows + 10`  in mpmath nothing
> changes, putting it in sympy it increases the
> precision of norm(d,inf) in the test by 3 digits.
> If in mpmath in the test I increase `mp.dps` by `3` before calling
> `expm(a1, method='pade')` the precision of norm(d,inf) in the test
> increases by 3 digits.
> What am I doing wrong?

I don't know. I tried adding " + 10" as above and it decreased
norm(d,inf) in the test. All tests currently pass for me.

Fredrik