Alan Chang's profile - activity

Hi,

To import a function you need to use a syntax like

from the_module import my_function

in your case it will be

from sage.gsl.integration import numerical_integral

To find out where is what, there is a magic function in Sage

sage: import_statements(numerical_integral)
from sage.gsl.integration import numerical_integral

(Note that the code you wrote won't run faster with cython: the function call will be in Cython but what is inside numerical_integral won't be different from a python call).

Thanks! Wow, import_statements() is amazing!. Yes, I realized that this wouldn't be faster. I just wanted to give a stand-alone example of calling Sage functions from Cython. (In my code, apart from Sage functions, there are other blocks which I believe would speed up with Cython.)

I am playing around with Cython but I can't get it to work very well with Sage. As a very simple example of the problems I am having, the following code doesn't work. I know that the reason is that I need to import numerical_integral() from Sage somehow, but I don't know exactly how to do that.

%cython

numerical_integral(x^2, 0,1)

(This is something that's been confusing me for a few days now. I'm not sure if there's something about how Cython is supposed to be used that I am not understanding properly.)

EDIT: after trying out some things, I realized that sage.gsl.integration.numerical_integral() has the same effect as numerical_integral() in Sage. So, somehow, I should import the function from sage.gsl.integration, if that even makes any sense?

Thank you!

The method .sort() sorts the list eval_args on place (i mean it modifies the list eval_args), it does not return a sorted copy of eval_args (it returns nothing, hence your behaviour):

sage: evals = Mat(CDF,10).random_element().eigenvalues()
sage: eval_args = map(arg, evals)
sage: eval_args
[-2.88140694172,
 2.66782234593,
 -0.206748063577,
 -0.663492557653,
 -1.34361452031,
 -1.67041594451,
 -2.22990648845,
 0.643653522447,
 1.5894324166,
 1.28058620418]
sage: eval_args.sort()
sage: eval_args
[-2.88140694172,
 -2.22990648845,
 -1.67041594451,
 -1.34361452031,
 -0.663492557653,
 -0.206748063577,
 0.643653522447,
 1.28058620418,
 1.5894324166,
 2.66782234593]

As you can see, after calling eval_args.sort(), the list eval_args is sorted.

If you do not want your list eval_args to be modified and get a sorted copy of it, just use the function sorted():

sage: evals = Mat(CDF,10).random_element().eigenvalues()
sage: eval_args = map(arg, evals)
sage: eval_args
[1.77315647525,
 2.73584430085,
 0.678473279316,
 1.0691046262,
 -0.229457152027,
 -2.26775012586,
 -2.35863979204,
 -1.30207117624,
 -2.75762912811,
 -0.789539732054]
sage: sorted(eval_args)
[-2.75762912811,
 -2.35863979204,
 -2.26775012586,
 -1.30207117624,
 -0.789539732054,
 -0.229457152027,
 0.678473279316,
 1.0691046262,
 1.77315647525,
 2.73584430085]
sage: eval_args        
[1.77315647525,
 2.73584430085,
 0.678473279316,
 1.0691046262,
 -0.229457152027,
 -2.26775012586,
 -2.35863979204,
 -1.30207117624,
 -2.75762912811,
 -0.789539732054]

As you can see, the list eval_args was not modified by the function sorted(). Unfortunately, there is no .sorted() method for lists.

I am using SAGE to calculate the arguments of the eigenvalues of a randomly-generated matrix. Here is my code.

evals = Mat(CDF,10).random_element().eigenvalues()
eval_args = map(arg, evals)
print eval_args.sort()

For some reason, the call to .sort() does not work, and what is printed is "None." Why does this happen?