220 11601 article Path: news.gmane.org!not-for-mail From: Jim Porter Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Proposal. Generators of numeric sequences: the steps class template Date: Sat, 28 Jun 2014 13:34:21 -0500 Lines: 51 Approved: news@gmane.org Message-ID: References: <8aec4acb-2eea-4288-b215-81e828cd0b42@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed X-Trace: ger.gmane.org 1403982918 21424 80.91.229.3 (28 Jun 2014 19:15:18 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 28 Jun 2014 19:15:18 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDYZZG6PQYFRBPFIXSOQKGQEGIOANWI@isocpp.org Sat Jun 28 21:15:12 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wi0-f199.google.com ([209.85.212.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1X0y5g-0005Xv-H1 for gclcip-std-proposals@m.gmane.org; Sat, 28 Jun 2014 21:15:12 +0200 Original-Received: by mail-wi0-f199.google.com with SMTP id n15sf2962142wiw.6 for ; Sat, 28 Jun 2014 12:15:12 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:user-agent:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=IXo6iK3Bwor7cB4iux/zu68iP8vYZ4j8dLHvtm213DQ=; b=QmXGPL2B0qjROphFrVl8QGuYFvslwjT8/n+lUBDWH28tn2UL6l9FyCI2fH4x1KDS8r frb/RQ6P0qHZA/DaKMSfXfHnOWuRUSfh34hoXdbICoZCdKnwZm4XoAYYQcpQBR5yYvEQ 0ZEM+cIJ0iQFWgnkq4jwvt84n0bNwNf/IUKnCd58DNqakUVuhgfecUerJv26JKprIhNV pXtzSM1byke+ULgd9PVPfh48m32YIZLVwEqRfRDo3feBpNsNgfKvMeQ0VuiNyIdRaiiG Cohl1fALRsffyaIDYh5gnsNKL+Kx9oXy7JisGul6cWoSp+bMoipNsi+LZU7ggvofljg5 7Kyw== X-Gm-Message-State: ALoCoQmJI2Qp9d/W9IvW54KMXgdIcktq0385sRPfO9dz1mfyJFcpnYN1vjeMcl39Td8LZFwxzvAX X-Received: by 10.112.163.195 with SMTP id yk3mr3177lbb.20.1403982912179; Sat, 28 Jun 2014 12:15:12 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.36.133 with SMTP id q5ls193484laj.12.gmail; Sat, 28 Jun 2014 12:15:07 -0700 (PDT) X-Received: by 10.112.210.9 with SMTP id mq9mr21338671lbc.47.1403982907704; Sat, 28 Jun 2014 12:15:07 -0700 (PDT) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id be5si26076597lbc.32.2014.06.28.12.15.07 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Sat, 28 Jun 2014 12:15:07 -0700 (PDT) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1X0y5X-0005T9-KM for std-proposals@isocpp.org; Sat, 28 Jun 2014 21:15:03 +0200 Original-Received: from 71-87-112-150.dhcp.mdsn.wi.charter.com ([71.87.112.150]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sat, 28 Jun 2014 21:15:03 +0200 Original-Received: from jvp4846 by 71-87-112-150.dhcp.mdsn.wi.charter.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sat, 28 Jun 2014 21:15:03 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 42 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 71-87-112-150.dhcp.mdsn.wi.charter.com User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 In-Reply-To: <8aec4acb-2eea-4288-b215-81e828cd0b42@isocpp.org> X-Original-Sender: jvp4846@g.rit.edu X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mail=gclcip-std-proposals@m.gmane.org Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:11601 Archived-At: On 6/28/2014 10:50 AM, Mikhail Semenov wrote: > https://dl.dropboxusercontent.com/u/35715999/steps_template.htm In this, you describe ways to use std::steps with floating point values, which requires some special handling to stop the iteration if you're within epsilon of the endpoint. However, for the floating point case, I'd really recommend using something more like NumPy's linspace, which takes, a start, a stop, and a *number of samples*. Supposing we had a function like template std::linspace(T start, T stop, size_t num, include_endpoint = true) and a corresponding std::make_linspace, this is how you could write your integrate function: double integrate( std::function f, double a, double b, int N ) { double h = (b - a) / N; double h2 = h * 0.5; double sum = 0.0; for(auto x : std::make_linspace(a + h2, b - h2, N)) { sum += f(x); } return sum * h; } This allows you to avoid worrying about how to define epsilon so that you're guaranteed to get the number of steps you expect. The extra complexity for the user is minimal, and makes it clearer that you expect N steps. If you cared less about efficiency, you could make the loop look even simpler: for(auto x : std::make_linspace(a, b, N, false)) { sum += f(x + h2); } Even with the epsilon calculation for std::steps, I'd still be worried about using it if I expected a particular number of iteration steps, and if that number were quite large. std::linspace would have no such trouble. - Jim -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. .