[Tutor] constructing semi-arbitrary functions

[Oscar Benjamin]

On 17 February 2014 21:18, "André Walker-Loud <walksloud at gmail.com>"
<walksloud at gmail.com> wrote:
>
> What I am trying to avoid is having to write a special case for each order of polynomial I want.  I tried the following
>
> def poly(x,pars):
>     val = 0.
>     for i,ci in enumerate(pars):
>         val += x**i * ci
>     return val
> def f_lambda(x,pars):
>     return lambda x,*pars: poly(x,*pars)
> x = np.array([1,2,3])
> f = f_lambda(x,[-.5,2.])
> f(x,[-.5,2.])
> array([ 1.5,  3.5,  5.5])
>
> f(x,[-.5,3.])
> array([ 2.5,  5.5,  8.5])
> etc.
>
> This function correctly gives me a polynomial of arbitrary order, but
>
> f.func_code.co_varnames
> ('x', 'pars')
>
> so I can not pass this to the third party minimizer, as it does not know how to interpret 'pars'.  You can probably see trying to replicate the lambda function method for an arbitrary polynomial is what naturally led to the string/exec option.

This particular case is easily solved:

def f_lambda(x,pars):
     return lambda x: poly(x,*pars)

You let the closure take care of pars and return a function that takes
exactly one argument x.


Oscar