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  • TripletLoss

    2021-01-29 19:54:37
    TripletLoss 最初是在《FaceNet: A Unified Embedding for Face Recognition and Clustering》這篇論文中所提出的 可以学到较好的人脸的特征值(embedding) 和SoftMax相比TripletLoss 更适合训练差异性较小的样本...

    TripletLoss

    什麼是TripletLoss?

    TripletLoss 最初是在《FaceNet: A Unified Embedding for Face Recognition and Clustering》這篇論文中所提出的

    可以学到较好的人脸的特征值(embedding)

    和SoftMax相比TripletLoss 更适合训练差异性较小的样本(比如判断人脸相似度)

    TripletLoss是如何实现的呢?

    • 首先,我们从训练数据中随机选择一个样本,我们暂且称这个样本是Anchor(锚)(x_a)
    • 第二步,我们再从数据集中选择一个与Anchor同属于同一个类别的样本,称这个样本为:Positive(x_p)
    • 第三步,我们再从数据集中选择一个与Anchor不同属于一个类别的样本,称这个样本为:Negative(x_n)
    • 第四步,我们将这三个元素构成一个三元组(triplet):<Anchor, Positive, Negative>
    • 第五步,我们通过优化锚示例与正示例的距离小于锚示例与负示例的距离,来实现样本的相似性计算

    triplet Loss的目的就是通过学习,让x_a和x_p之间的距离尽可能的小,让x_a和x_n之间的距离尽可能的大在这里插入图片描述

    至此我们就基本了解了TripletLoss的工作原理,那么在深度学习框架中是如何进行推导的呢?

    通过上诉我们对TripletLoss的公式的理解,我们可以推出公式如下所示:

    L=max(d(xa,xp)d(xa,xn)+margin,0)L = max(d(x_a, x_p) - d(x_a, x_n) + margin, 0)

    我们可以从上面的公式进行推导

    • easy triplets : 当L = 0时, 说明,d(xa,xp)+margin<d(xa,xn)d(x_a, x_p) + margin < d(x_a, x_n), 这种情况就是我们所需要的情况
    • hard triplets :d(xa,xn)<d(xa,xp)d(x_a, x_n)<d(x_a, x_p) 这种情况是我们需要训练的情况
    • semi-hard triplets :d(xa,xp)<d(xa,xn)<d(xa,xp)+margind(x_a, x_p)<d(x_a, x_n)<d(x_a, x_p)+margin 这种情况,也是我们需要训练的情况,其中,论文中所用的训练模式就是这个情况

    论文中TripletLoss的公式为:

    L=argmini=1i=n(xiaxip2xiaxin2+threshold)+L = argmin\sum_{i=1}^{i=n}(||x^a_i - x^p_i||^2 - ||x^a_i - x^n_i||^2 + threshold)_+

    公式中左下角的+号表示的是:只有括号内公式的值大于0时,我们才计算误差

    Triplet Loss的使用

    import torch
    import torch.nn as nn
    triplet_loss = nn.TripletMarginLoss(margin=1.0)
    input1 = torch.randn(100, 128)  # x_a  image1
    input2 = torch.randn(100, 128)  # x_p  image2
    input3 = torch.randn(100, 128)  # x_n  image3
    output = triplet_loss(input1, input2, input3)
    output
    

    运行结果

    tensor(1.2242)
    

    对手写数字进行分类
    在这里插入图片描述

    展开全文
  • Problem 9Special Pythagorean tripletA Pythagorean triplet is a set of three natural numbers, a &lt; b &lt; c, for which,a2 + b2 = c2For example, 32 + 42 = 9 + 16 = 25 = 52.There exists ...

    Problem 9


    Special Pythagorean triplet

    A Pythagorean triplet is a set of three natural numbers, a < b < c, for which,

    a2 + b2 = c2

    For example, 32 + 42 = 9 + 16 = 25 = 52.

    There exists exactly one Pythagorean triplet for which a + b + c = 1000.Find the product abc.


    特殊毕达哥拉斯三元组

    毕达哥拉斯三元组是三个自然数a < b < c组成的集合,并满足

    a2 + b2 = c2

    例如,32 + 42 = 9 + 16 = 25 = 52

    有且只有一个毕达哥拉斯三元组满足 a + b + c = 1000。求这个三元组的乘积abc。

    题目解答

       朴素解法:暴力枚举
       优化算法:我们利用素勾股数的相关性质来构造合勾股数来解决这个问题。
        
       素勾股数

                    性质 1. 他们整数倍也是勾股数,即(na, nb, nc)也是勾股数。

                    性质 2. (a, b, c)之间两两互质。

                    性质 3. a, b必为一奇一偶。

                    性质 4. 任何素勾股数均可表示为如下形式, 其中 n < m, 且 gcd(n, m) = 1

                                    a = 2 * n * m

                                    b = m^2 - n^2

                                    c  = m^2 + n^2 

    题目代

    #include <stdio.h>
    #include <inttypes.h>
    #include <stdlib.h>
    #include <math.h>
    int gcd(int a,int b){return !b?a:gcd(b,a%b);}
    int main() {
        bool flag = true;
        int32_t a, b, c, e;
        for (int32_t i = 1; i < 32 && flag; ++i) {
            for (int32_t j = i + 1; j <= 32 && flag; ++j) {
                if((i % 2 == 0 && j % 2 !=0)||(i % 2 != 0 && j % 2 == 0)){
                    if(gcd(i,j)!=1)continue;
                    a = j * j - i * i;
                    b = 2 * i * j;
                    c = i * i + j * j;
                    if (1000 % (a + b + c) == 0) {
                        e = (int32_t)pow(1000 / (a + b + c), 3);
                        printf("%d\n", e * a * b * c);
                        flag = false;
                    }
                }
            }
        }
        return 0;
    }

    展开全文
  • Pythagorean Triplet

    2020-11-24 14:20:18
    The methods will check if a pythagorean triplet exists / if the passed in parameters are triplets. <h3>Have you read the Contribution Guidelines? <p>Yes <h2>Pitch <p>This is just an algorithm used to...
  • Triplet Loss

    千次阅读 2018-08-08 15:50:36
    Triplet Loss 三元组(Triplet)计算而来的损失(Loss) 由Anchor(A),Negative(N),Positive(P)组成,基点为A,正匹配为P,负匹配为N。 Triplet Loss的学习目标可以形象的表示如下图: 网络没经过学习之前,A...

    Triplet Loss

    三元组(Triplet)计算而来的损失(Loss)

    由Anchor(A),Negative(N),Positive(P)组成,基点为A,正匹配为P,负匹配为N。

    Triplet Loss的学习目标可以形象的表示如下图:

    网络没经过学习之前,A和P的欧式距离可能很大,A和N的欧式距离可能很小,如上图左边,在网络的学习过程中,A和P的欧式距离会逐渐减小,而A和N的距离会逐渐拉大。

    网络会直接学习特征间的可分性:同一类的特征之间的距离要尽可能的小,而不同类之间的特征距离要尽可能的大。

    通过学习,使得类间的距离要大于类内的距离。

    损失函数为:

    其中,左边的二范数表示类内距离,右边的二范数表示类间距离,α是一个常量。优化过程就是使用梯度下降法使得损失函数不断下降,即类内距离不断下降,类间距离不断提升。

    Hard Triplets

    理论上说,为了保证网络训练的效果最好,我们要选择hard positive

    以及hard negative

    来作为我们的三元组

    Hard Triplets应该是满足类内距离最大化并且类间距离最小化的三元组。

     

     

    展开全文
  • projecteuler Problem 9 Special Pythagorean triplet ...A Pythagorean triplet is a set of three natural numbers, a < b < c, for which, a2 + b2 = c2 For example, 32 +...

    A Pythagorean triplet is a set of three natural numbers, a < b < c, for which,

    a2 + b2 = c2

    For example, 32 + 42 = 9 + 16 = 25 = 52.

    There exists exactly one Pythagorean triplet for which a + b + c = 1000.
    Find the product abc.

    译文:一个毕达哥拉斯三元数组是由三个自然数组成,a<b<c,形如

    举个例子,32 + 42 = 9 + 16 = 25 = 52.

    现在存在一个毕达哥拉斯三元数组,它满足 a + b + c = 1000.毕达哥拉斯三元数组的数值乘积。

     


    第一次code:

     1 public class Main
     2 { 
     3     public static void main(String[] args) 
     4     { 
     5         System.out.println(run(1000));
     6     }
     7     public static String run(int n)
     8     {
     9         String a="";
    10         for(int i=1;i<n;i++)
    11         {
    12             for(int j=0;j<i;j++)
    13             {
    14                 for(int s=0;s<j;s++)
    15                 {
    16                     if(s*s+j*j==i*i)
    17                     {
    18                          if(s+j+i == 1000)
    19                          {
    20                              a =String.valueOf(s*j*i);
    21                          }
    22                     }
    23                 }
    24             }
    25         }
    26         return a;
    27     }
    28 }

    时间效率:280毫秒。

    posted on 2016-08-29 16:07 niithub 阅读(...) 评论(...) 编辑 收藏

    转载于:https://www.cnblogs.com/niithub/p/5818394.html

    展开全文
  • <div><p>With this the <code>key</code> field will be like <code>#{key => resolver_crash, ...}</code> instead of returning <code>#{key => {resolver_crash, <<"...
  • <div><p>Hi, thanks for the excellent work, it helps me a lot. Because I need to deploy the model in my project, so I made a simple wrapper to do human ...VisualComputingInstitute/triplet-reid</p></div>
  • A Pythagorean triplet is a set of three natural numbers, {a, b, c}, for which, <code>a**2 + b**2 = c**2 For example, <code>3**2 + 4**2 = 9 + 16 = 25 = 5**2</code>. There ...
  • <div><p>In Python, <code>Ivis.__init__</code> accepts a <code>distance: str</code> keyword argument, which sets from a dictionary a predefined triplet loss function for that distance metric....
  • Triplet Selection

    2018-01-31 21:35:00
    title: Triplet Selection grammar_cjkRuby: true --- 样本选取的理想情况: a minimal number of exemplars of any one identity is present in each mini-batch 单个个体的全部样本必须存在于每个mini-batch...
  • <div><p>This PR makes a small change to the mixed triplet seed layers to become consistent with the detached triplet seed layers and cuts. <p>There are also updates to improve the behavior of the MVA ...
  • Beyond triplet loss: a deep quadruplet network for person re-identification CVPR2017 https://arxiv.org/abs/1704.01719本文使用深度学习进行行人检索,侧重点主要在损失函数的改进,提出了 quadruplet loss ...
  • <div><p>[This is a summary of things discussed in trac.766] Neurons have the property tau_minus_triplet, but this does not seem to be used, which may be confusing for users. In the ticket triage ...
  • Triplet loss test

    2020-11-28 09:26:11
    <div><p>Some users reported that the program would crash when using triplet loss... Can someone have a try and report the result to me?</p><p>该提问来源于开源项目:happynear/caffe-windows</p></div>
  • A 360° light field 3D display system is presented, which consists of a liquid crystal display, a novel triplet lenses array, and a holographic functional screen (HFS). The mapping relationship among ...
  • 032 Pythagorean Triplet

    2020-10-07 04:24:30
    test if any consecutive triplet can form the length of edges that combines as a Pythagorean. this problem is so simple that i don’t even needs to provide answers here. just iterate all whole array
  • Special Pythagorean triplet

    2014-05-08 13:35:00
    A Pythagorean triplet is a set of three natural numbers, a b c, for which, a2 + b2 = c2 For example, 32 + 42 = 9 + 16 = 25 = 52. There exists exactly one Pythagorean triplet for...
  • Fix tripletLoss

    2021-01-09 13:56:34
    <p><code>return self.batch_hard_triplet_loss(labels, reps[0]) My fix ignore the situation which use label as <code>the true distance between instances, like the implement in #448 <p>I have not tested ...
  • standardize host triplet

    2020-12-09 06:55:28
    Instead, a proper host triplet such as "powerpc64-ps3-elf" should be used. Symlinks called "ppu-*" can be created to provide backwards compatibility. <p>"spu" on the other ...
  • Triplet Loss入门

    千次阅读 2018-12-10 14:39:36
    Triplet Loss入门 Face verification vs. face recogntion Verification Input image, name/ID Output whether the input image is that of the claimed person. Recognition Has a database of K peosons(or...
  • A Pythagorean triplet is a set of three natural numbers,a<b<c, for which, a²+b²=c² For example, 3²+ 4²= 9 + 16 = 25 = 5². There exists exactly one Pythagorean triplet for whicha+...
  • <div><p><strong> The following layers are ...RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn</p><p>该提问来源于开源项目:KaiyangZhou/deep-person-reid</p></div>
  • 文章目录概述方法The triplet lossThe quadruplet lossRelationships of different lossescontrastive loss 概述 三元损失训练的模型泛化能力不强,类内方差依然较大,作者提出四元损失函数,用于减小类内方差 和 ...
  • TRB: A Novel Triplet Representation for Understanding 2D Human Body ICCV 2019 paper :https://arxiv.org/pdf/1910.11535.pdf 论文介绍了一种新的人体特征表示方法(TRB->Triplet Representation for ...

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