Dear Henri,
When you do
import numpy as np
you are just creating a identifier that allows you to reach for a numpy
function that happens to have the same name as another Sage|Python
function. You do nor "import" physically anything.
So when you do :
foo=<whatever>
sqrt(foo)
you are in fact calling the Sage function sqrt, with the argument <whatever>
; that may or may not make sense to Sage.
But if you do
foo=np.<something>()
np.sqrt(foo)
you are calling the Numpy function sqrt, with an argument which is
(probably) a Numpy object. np.sqrt(foo) may make sense (as opposed to, say,
np.sqrt(bar), where bar is something without relation to Numpy...).
Le mardi 9 janvier 2018 14:33:53 UTC+1, HG a écrit :
>
> Nothing goes wrong : My question is sage has already lot of functions
> which don't need numpy, but if there is one function which needs numpy I
> will have to add it.
Indeed. And you should note that this Numpy function may return something
that is a Numpy object, that other Sage functions may or may not be able to
use. You may have to convert it back to Sage.
A better example is given by Sympy. You may want to use, for example, its
Laplace transform (and inverse thereof), which seem somewhat more capable
than the native (Maxima's) one, or its Fourier transforms (which do not
even exist in Maxima...).
import sympy
f=<some function of t>
var("s,t")
st,ss=sympy.symbols("st,ss")
F=sympy.fourier__transform(sympy.sympify(f),ss,st)
G=<somethingInterestingInvolvingF>
g=sympy.inverse_fourier_transform(G,st,ss)
At this point, g is something composed of sympy objects (IIRC, a tuup,e,
whose first element is the sought inverse Fourier transform). In order to
use it in Sage, you have to transform it back (using the ._sage_() method)
and possibly rename some variables.
This mechanism has been automated for some operations : for example, that's
(very roughly !) what the 'algorithm="sympy"' option of integrate() does.
> And arange needs np then I am asking if there a way
> to do it in sage without using numpy,
So in fact, you are looking for a "pure Sage" implementation of arange(). I
do not know what does arange : it migh be trivial it might verge on the
impossible, I do not know.
But the point is that mechanisms (which is relatively cheap) offers you a
lot of power and flexibility : you can use the arange algorithm even if
iot's not implemented|implementable in Sage...
Furthermore, you should consider if you need you result as a Sage object.
For your purposes, in may be that (a part of) your algorithm is easier to
express with Numpy ; so may be interested by implementing this part with
Numpy and convert back to Sage only what you want in Sage...
--
Emmanuel Charpentier
> I am not an expert in sage and I
> try to keep to pure command, I don't like to import lot of libs as they
> are already declare in sage, I think is redondant... Then I just wanted
> to know if there a way of doing np.arange but only with sage (not
> importing numpy), for example matplolib uses lot of declaration like
> plt... when i do a plot I only use plot(), I prefer look to sage plot
> commands (even if they are from matplotlib) that's why I appreciate
> sage, for latex it's very easy to have it straight because the libs are
> in sage. I use sage to do lot of work maths graphs draw music ... etc,
> then I just add them with sage -pip and after I have nothing to remenber
> for me sage is a kind of wisiwigsage all-in-one. I am a user not a
> developer (pity for me... I would like to know this better), sage is the
> best tool for math in my way. Easy, well documented and much more... I
> do a lot of things (maybe not academic) but suiting to my needs... At
> the moment I am in antic chinese music and this requires geometry /
> music / math... sage do all :)
>
> Regards
>
> Henri
>
>
>
> Le 09/01/2018 à 13:34, Simon King a écrit :
> > Hi,
> >
> > On 2018-01-09, Girard Henri <henri....@gmail.com <javascript:>> wrote:
> >> Am 09.01.2018 um 12:18 schrieb Girard Henri:
> >>> An exemple
> >>>
> >>> from matplotlib import pyplot as plt
> >>> from scipy.io import wavfile
> >>> import numpy as np
> >>> samplerate,data=wavfile.read("test.wav")
> >>> times=np.arange(len(data))/float(samplerate)
> >>> plt.plot(data[:1000])
> > What exactly goes wrong if you do the above in Sage? Please be more
> > specific.
> >
> > In another message to me, you wrote:
> >> Most of the time I don't want to make heavier "import"... First because
> >> I don't master it and it's much better to do sqrt() instead np.sqrt()
> or
> >> np.pi()
> > I don't see why sqrt() is better than np.sqrt().
> >
> > Anyway, as usual in Python, you can import functions like this:
> > sage: from numpy import sqrt
> > sage: sqrt
> > <ufunc 'sqrt'>
> > sage: sqrt(4)
> > 2.0
> > sage: type(_)
> > <type 'numpy.float64'>
> >
> > The disadvantage is that it overwrites Sage's sqrt() function. That's
> why
> > I believe it is better to do np.sqrt().
> >
> > Best regards,
> > Simon
> >
>
>
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