python - Avoid creating new arrays as results for numpy/scipy operations? -


for doing repeated operations in numpy/scipy, there's lot of overhead because operation return new object.

for example

for in range(100):    x = a*x

i avoid passing reference operation, in c

for in range(100):    np.dot(a,x,x_new) #x_new store result of multiplication    x,x_new = x_new,x

is there way this? not mutiplication operations return matrix or vector.

see learning avoid unnecessary array copies in ipython books. there, note e.g. these guidelines:

a *= b

will not produce copy, whereas:

a = * b

will produce copy. also, flatten() copy, while ravel() copies if necessary , returns view otherwise (and should in general preferred). reshape() not produce copy, returns view.

furthermore, @hpaulj , @ali_m noted in comments, many numpy functions support out parameter, have @ docs. numpy.dot() docs:

out : ndarray, optional output argument.

this must have exact kind returned if not used. in particular, must have right type, must c-contiguous, , dtype must dtype returned dot(a,b). performance feature. therefore, if these conditions not met, exception raised, instead of attempting flexible.


Comments

Post a Comment

Popular posts from this blog

python - Installing PyDev in eclipse is failed -

unable read repository @ http://pydev.sf.net/updates/content.xml. sun.security.validator.validatorexception: pkix path building failed: sun.security.provider.certpath.suncertpathbuilderexception: unable find valid certification path requested target i installing pydev in eclipse using python, doesn't install successfully. gives above error. happened? how solve error? i had error when trying install on laptop behind corporate firewall. couldn't tell setup of firewall, not sure of root cause. i got passed error installing pydev eclipse when out behind firewall. another way got around have eclipse on non-firewalled machine, install pydev eclipse, , copy whole eclipse directory non-firewalled machine firewalled machine. there better way, , way fix properly, didn't have time work out firewall doing. this on windows 7 machine (yeah know) not work *nix versions installed through package manager yum or apt.
Read more

PHP OOP-based login system -

lets building oop-based user authentication system, , incorporate following principles: direct injection, inheritance, encapsulation, polymorphism , single responsibility principle. my background in programming has relied on procedural programming, , thus, finding difficult put these practices correct use. assume have these classes: class config { public function set($key, $value); public function get($key, $default = null); } class user { public function __construct(pdo $dbh, $id = null); public function setprofile(profile $profile); } class auth { public function __construct(config $config); public function login($username, $password, $keeploggedin = true); public function isloggedin(); public function getloggedinuser(); public function logout(); public function register(array $data); } class session { public function start($sessionname = null); public function write($key, $value); public function read($key, $default =...
Read more

c# - Nested Internal Class with Readonly Hashtable throws Null ref exception.. on assignment -

in internal game class , have both a) defined nested internal gamertags class , b) defined gamertags[] _array variable. in internal gamertags class (the nested class, simplicity left out) have readonly hashtable . after initialization, still null ref exception when try assign value. i'm not changing pointer value only , need add initialization hastable? internal class gamertags { private readonly hashtable _privatereadonlyhashtable; private string _json; private string _hash; internal idictionary privatereadonlyhashtable { { return this._privatereadonlyhashtable; } } internal string hash { { this.ensurehash(); return this._hash; } } internal object this[string key] { { return this._privatereadonlyhashtable[k...
Read more