Performance 加权Gram-Schmidt正交化的MATLAB优化
我在MATLAB中有一个函数,它通过对内积应用非常重要的权重来执行计算(我认为MATLAB的内置函数不支持这一点)。 就我所知,这个函数工作得很好,但是,它在大型矩阵上太慢了。 改善这一点的最佳方法是什么 我尝试过转换成一个MEX文件,但我失去了与我正在使用的编译器的并行化,因此速度会变慢 我想在GPU上运行它,因为元素乘法是高度并行的。(但我更希望实现易于移植) 任何人都可以将此代码矢量化或使其更快吗?我不知道如何优雅地做这件事 <> P>我知道这里的堆栈溢出的想法令人惊叹,认为这是一个挑战: 功能 其中,Performance 加权Gram-Schmidt正交化的MATLAB优化,performance,matlab,optimization,linear-algebra,vectorization,Performance,Matlab,Optimization,Linear Algebra,Vectorization,我在MATLAB中有一个函数,它通过对内积应用非常重要的权重来执行计算(我认为MATLAB的内置函数不支持这一点)。 就我所知,这个函数工作得很好,但是,它在大型矩阵上太慢了。 改善这一点的最佳方法是什么 我尝试过转换成一个MEX文件,但我失去了与我正在使用的编译器的并行化,因此速度会变慢 我想在GPU上运行它,因为元素乘法是高度并行的。(但我更希望实现易于移植) 任何人都可以将此代码矢量化或使其更快吗?我不知道如何优雅地做这件事 P>我知道这里的堆栈溢出的想法令人惊叹,认为这是一个挑战: 功
A
是复数的mxn
矩阵,w
是实数的mx1
向量
瓶颈
这是函数最慢部分的R(i,j)
的表达式(不100%确定符号是否正确):
其中,w
是一个非负权重函数。
加权内积在几个维基百科页面上都有提及,并且
复制
可以使用以下脚本生成结果:
A = complex( rand(360000,100), rand(360000,100));
w = rand(360000, 1);
[Q, R] = Gram_Schmidt(A, w);
A = complex( rand( 100, 10), rand( 100, 10));
w = rand( 100, 1);
[Q , R ] = Gram_Schmidt( A, w);
[Q2, R2] = Gram_Schmidt2( A, w);
zeros1 = norm( Q - Q2 );
zeros2 = norm( R - R2 );
其中A
和w
是输入
速度和计算
如果使用上述脚本,您将获得与以下内容同义的探查器结果:
测试结果
通过使用以下脚本将函数与上述函数进行比较,可以测试结果:
A = complex( rand(360000,100), rand(360000,100));
w = rand(360000, 1);
[Q, R] = Gram_Schmidt(A, w);
A = complex( rand( 100, 10), rand( 100, 10));
w = rand( 100, 1);
[Q , R ] = Gram_Schmidt( A, w);
[Q2, R2] = Gram_Schmidt2( A, w);
zeros1 = norm( Q - Q2 );
zeros2 = norm( R - R2 );
其中,Gram_-Schmidt
是前面描述的函数,Gram_-Schmidt2
是替代函数。结果zeros1
和zeros2
应该非常接近于零
注意:
我试着用以下方法加速计算R(I,j)
,但没有用
R(i,j) = ( w' * ( v .* conj( Q(:,i) ) ) ) / ...
( w' * ( Q(:,i) .* conj( Q(:,i) ) ) );
1)
我第一次尝试矢量化:
function [Q, R] = Gram_Schmidt1(A, w)
[m, n] = size(A);
Q = complex(zeros(m, n));
R = complex(zeros(n, n));
for j = 1:n
v = A(:,j);
QQ = Q(:,1:j-1);
QQ = bsxfun(@rdivide, bsxfun(@times, w, conj(QQ)), w.' * abs(QQ).^2);
for i = 1:j-1
R(i,j) = (v.' * QQ(:,i));
v = v - R(i,j) * Q(:,i);
end
R(j,j) = norm(v);
Q(:,j) = v / R(j,j);
end
end
不幸的是,它比原来的函数慢
2) 然后我意识到这个中间矩阵
QQ
的列是增量构建的,而之前的列没有修改。这是我的第二次尝试:
function [Q, R] = Gram_Schmidt2(A, w)
[m, n] = size(A);
Q = complex(zeros(m, n));
R = complex(zeros(n, n));
QQ = complex(zeros(m, n-1));
for j = 1:n
if j>1
qj = Q(:,j-1);
QQ(:,j-1) = (conj(qj) .* w) ./ (w.' * (qj.*conj(qj)));
end
v = A(:,j);
for i = 1:j-1
R(i,j) = (v.' * QQ(:,i));
v = v - R(i,j) * Q(:,i);
end
R(j,j) = norm(v);
Q(:,j) = v / R(j,j);
end
end
技术上没有进行重大的矢量化;我只预先计算了中间结果,并将计算移到了内部循环之外
基于快速基准测试,此新版本绝对更快:
% some random data
>> M = 10000; N = 100;
>> A = complex(rand(M,N), rand(M,N));
>> w = rand(M,1);
% time
>> timeit(@() Gram_Schmidt(A,w), 2) % original version
ans =
1.2444
>> timeit(@() Gram_Schmidt1(A,w), 2) % first attempt (vectorized)
ans =
2.0990
>> timeit(@() Gram_Schmidt2(A,w), 2) % final version
ans =
0.4698
% check results
>> [Q,R] = Gram_Schmidt(A,w);
>> [Q2,R2] = Gram_Schmidt2(A,w);
>> norm(Q-Q2)
ans =
4.2796e-14
>> norm(R-R2)
ans =
1.7782e-12
编辑: 在注释之后,我们可以重写第二个解决方案,通过将该部分移动到外循环的末尾(即,在计算新列
Q(:,j)
之后,我们计算并存储相应的QQ(:,j)
)
输出功能相同,定时也没有什么不同;代码只是稍微短一点
function [Q, R] = Gram_Schmidt3(A, w)
[m, n] = size(A);
Q = zeros(m, n, 'like',A);
R = zeros(n, n, 'like',A);
QQ = zeros(m, n, 'like',A);
for j = 1:n
v = A(:,j);
for i = 1:j-1
R(i,j) = (v.' * QQ(:,i));
v = v - R(i,j) * Q(:,i);
end
R(j,j) = norm(v);
Q(:,j) = v / R(j,j);
QQ(:,j) = (conj(Q(:,j)) .* w) ./ (w.' * (Q(:,j).*conj(Q(:,j))));
end
end
注意,我使用了zero(…,'like',A)
语法(在最近的MATLAB版本中是新的)。这允许我们在GPU上不经修改地运行函数(假设您拥有并行计算工具箱):
vs
不幸的是,在我的情况下,它没有任何更快。事实上,在GPU上运行要比在CPU上运行慢很多倍,但值得一试:)这里有一个很长的讨论,但是,要跳到答案上来。你已经用向量w加权了R计算的分子和分母。加权发生在内环上,由三点积、分子中的点Q点w和分母中的点Q点w组成。如果您做一个更改,我认为代码将运行得更快。写入num=(A点sqrt(w))点(Q点sqrt(w))和写入den=(Q点sqrt(w))点(Q点sqrt(w))。这将(A点sqrt(w))和(Q点sqrt(w))乘积计算移出内部循环 我想对Gram-Schmidt正交化的公式进行描述,希望除了给出另一种计算解决方案外,还能进一步深入了解GSO的优势 GSO的“目标”有两个方面。首先,要解决Ax=y这样的方程,其中A的行远多于列。这种情况在测量数据时经常发生,因为测量的数据很容易超过状态数。实现第一个目标的方法是将A重写为QR,使得Q的列是正交的和规范化的,并且R是三角矩阵。我相信,您提供的算法实现了第一个目标。Q表示矩阵的基空间,R表示生成A的每列所需的每个基空间的振幅 GSO的第二个目标是按照重要性的顺序对基础向量进行排序。这是您尚未完成的步骤。而且,虽然包括这一步骤,可能会增加求解时间,但结果将根据测量值中包含的数据确定x的哪些元素是重要的 但是,我认为,通过这种实现,解决方案比您提出的方法更快 Aij=Qij-Rij,其中Qj是正交的,Rij是上三角形,Ri,j>i=0。Qj是A的正交基向量,Rij是每个Qj在A中创建列的参与度。因此
A_j1 = Q_j1 * R_1,1
A_j2 = Q_j1 * R_1,2 + Q_j2 * R_2,2
A_j3 = Q_j1 * R_1,3 + Q_j2 * R_2,3 + Q_j3 * R_3,3
通过检查,你可以写
A_j1 = ( A_j1 / | A_j1 | ) * | A_j1 | = Q_j1 * R_1,1
然后每隔一列A将Q_j1投影到上,得到R_1,j元素
R_1,2 = Q_j1 dot Aj2
R_1,3 = Q_j1 dot Aj3
...
R_1,j(j>1) = A_j dot Q_j1
然后从A的列中减去Q_j1的project元素(这会将第一列设置为零,因此可以忽略第一列)
for j = 2,n
A_j = A_j - R_1,j * Q_j1
end
现在从A中删除一列,确定第一个正交基向量Q,j1,并确定第一个基向量对每列R_1,j的贡献,并从每列中减去第一个基向量的贡献。重复此步骤
for j = 2,n
A_j = A_j - R_1,j * Q_j1
end
for i = 1,n
R_ii = |A_i| A_i is the ith column of A, |A_i| is magnitude of A_i
Q_i = A_i / R_ii Q_i is the ith column of Q
for j = i, n
R_ij = | A_j dot Q_i |
A_j = A_j - R_ij * Q_i
end
end
w = w / | w |
for i = 1,n
R_ii = |A_i inner product w| # A_i inner product w = A_i .* w
Q_i = A_i / R_ii
for j = i, n
R_ij = | (A_i inner product w) dot Q_i | # A dot B = A' * B
A_j = A_j - R_ij * Q_i
end
end
A inner product B = A .* B
A dot w = A' w
(A B)' = B'A'
A' conj(A) = |A|^2
function [Q, R] = Gram_Schmidt_2(A, w)
[m, n] = size(A);
Q = complex(zeros(m, n));
R = complex(zeros(n, n));
# Outer loop identifies the basis vectors
for j = 1:n
aCol = A(:,j);
# Subtract off the basis vector
for i = 1:(j-1)
R(i,j) = ctranspose(Q(:,j)) * aCol;
aCol = aCol - R(i,j) * Q(:,j);
end
amp_A_col = norm(aCol);
R(j,j) = amp_A_col;
Q(:,j) = aCol / amp_A_col;
end
end
function [Q, R] = Gram_Schmidt_2(A, w)
[m, n] = size(A);
Q = complex(zeros(m, n));
R = complex(zeros(n, n));
# Outer loop identifies the basis vectors
for j = 1:n
aCol = A(:,j);
# Subtract off the basis vector
for i = 1:(j-1)
# R(i,j) = ctranspose(Q(:,j)) * aCol;
R(i,j) = sum( aCol .* conj( Q(:,i) ) .* w ) / ...
sum( Q(:,i) .* conj( Q(:,i) ) .* w );
aCol = aCol - R(i,j) * Q(:,j);
end
amp_A_col = norm(aCol);
R(j,j) = amp_A_col;
Q(:,j) = aCol / amp_A_col;
end
end
function [Q, R] = Gram_Schmidt_3(A, w)
[m, n] = size(A);
Q = complex(zeros(m, n));
R = complex(zeros(n, n));
Q_sw = complex(zeros(m, n));
sw = w .^ 0.5;
for j = 1:n
aCol = A(:,j);
aCol_sw = aCol .* sw;
# Subtract off the basis vector
for i = 1:(j-1)
# R(i,j) = ctranspose(Q(:,i)) * aCol;
numTerm = ctranspose( Q_sw(:,i) ) * aCol_sw;
denTerm = ctranspose( Q_sw(:,i) ) * Q_sw(:,i);
R(i,j) = numTerm / denTerm;
aCol_sw = aCol_sw - R(i,j) * Q_sw(:,i);
end
aCol = aCol_sw ./ sw;
amp_A_col = norm(aCol);
R(j,j) = amp_A_col;
Q(:,j) = aCol / amp_A_col;
Q_sw(:,j) = Q(:,j) .* sw;
end
end
function [Q, R] = Gram_Schmidt_4(A, w)
[m, n] = size(A);
Q = complex(zeros(m, n));
R = complex(zeros(n, n));
for j = 1:n
aCol = A(:,j);
for i = 1:(j-1)
cqw = conj(Q(:,i)) .* w;
R(i,j) = ( transpose( aCol ) * cqw) ...
/ (transpose( Q(:,i) ) * cqw);
aCol = aCol - R(i,j) * Q(:,i);
end
amp_A_col = norm(aCol);
R(j,j) = amp_A_col;
Q(:,j) = aCol / amp_A_col;
end
end
function Gram_Schmidt_tester_2
nSamples = 360000;
nMeas = 100;
nMeas = 15;
A = complex( rand(nSamples,nMeas), rand(nSamples,nMeas));
w = rand(nSamples, 1);
profile on;
[Q1, R1] = Gram_Schmidt_basic(A);
profile off;
data1 = profile ("info");
tData1=data1.FunctionTable(1).TotalTime;
approx_zero1 = A - Q1 * R1;
max_value1 = max(max(abs(approx_zero1)));
profile on;
[Q2, R2] = Gram_Schmidt_w_Orig(A, w);
profile off;
data2 = profile ("info");
tData2=data2.FunctionTable(1).TotalTime;
approx_zero2 = A - Q2 * R2;
max_value2 = max(max(abs(approx_zero2)));
sw=w.^0.5;
profile on;
[Q3, R3] = Gram_Schmidt_sqrt_w(A, w);
profile off;
data3 = profile ("info");
tData3=data3.FunctionTable(1).TotalTime;
approx_zero3 = A - Q3 * R3;
max_value3 = max(max(abs(approx_zero3)));
profile on;
[Q4, R4] = Gram_Schmidt_4(A, w);
profile off;
data4 = profile ("info");
tData4=data4.FunctionTable(1).TotalTime;
approx_zero4 = A - Q4 * R4;
max_value4 = max(max(abs(approx_zero4)));
profile on;
[Q5, R5] = Gram_Schmidt_5(A, w);
profile off;
data5 = profile ("info");
tData5=data5.FunctionTable(1).TotalTime;
approx_zero5 = A - Q5 * R5;
max_value5 = max(max(abs(approx_zero5)));
profile on;
[Q2a, R2a] = Gram_Schmidt2a(A, w);
profile off;
data2a = profile ("info");
tData2a=data2a.FunctionTable(1).TotalTime;
approx_zero2a = A - Q2a * R2a;
max_value2a = max(max(abs(approx_zero2a)));
profshow (data1, 6);
profshow (data2, 6);
profshow (data3, 6);
profshow (data4, 6);
profshow (data5, 6);
profshow (data2a, 6);
sprintf('Time for %s is %5.3f sec with %d samples and %d meas, max value is %g',
data1.FunctionTable(1).FunctionName,
data1.FunctionTable(1).TotalTime,
nSamples, nMeas, max_value1)
sprintf('Time for %s is %5.3f sec with %d samples and %d meas, max value is %g',
data2.FunctionTable(1).FunctionName,
data2.FunctionTable(1).TotalTime,
nSamples, nMeas, max_value2)
sprintf('Time for %s is %5.3f sec with %d samples and %d meas, max value is %g',
data3.FunctionTable(1).FunctionName,
data3.FunctionTable(1).TotalTime,
nSamples, nMeas, max_value3)
sprintf('Time for %s is %5.3f sec with %d samples and %d meas, max value is %g',
data4.FunctionTable(1).FunctionName,
data4.FunctionTable(1).TotalTime,
nSamples, nMeas, max_value4)
sprintf('Time for %s is %5.3f sec with %d samples and %d meas, max value is %g',
data5.FunctionTable(1).FunctionName,
data5.FunctionTable(1).TotalTime,
nSamples, nMeas, max_value5)
sprintf('Time for %s is %5.3f sec with %d samples and %d meas, max value is %g',
data2a.FunctionTable(1).FunctionName,
data2a.FunctionTable(1).TotalTime,
nSamples, nMeas, max_value2a)
end
ans = Time for Gram_Schmidt_basic is 0.889 sec with 360000 samples and 15 meas, max value is 1.57009e-16
ans = Time for Gram_Schmidt_w_Orig is 0.952 sec with 360000 samples and 15 meas, max value is 6.36717e-16
ans = Time for Gram_Schmidt_sqrt_w is 0.390 sec with 360000 samples and 15 meas, max value is 6.47366e-16
ans = Time for Gram_Schmidt_4 is 0.452 sec with 360000 samples and 15 meas, max value is 6.47366e-16
ans = Time for Gram_Schmidt_5 is 2.636 sec with 360000 samples and 15 meas, max value is 6.47366e-16
ans = Time for Gram_Schmidt2a is 0.905 sec with 360000 samples and 15 meas, max value is 6.68443e-16
function [Q, R] = Gram_Schmidt5(A, w)
Q = A;
n_dimensions = size(A, 2);
R = zeros(n_dimensions);
R(1, 1) = norm(Q(:, 1));
Q(:, 1) = Q(:, 1) ./ R(1, 1);
for i = 2 : n_dimensions
Qw = (Q(:, i - 1) .* w)' * Q(:, (i - 1) : end);
R(i - 1, i : end) = Qw(2:end) / Qw(1);
%% Surprisingly this loop beats the matrix multiply
for j = i : n_dimensions
Q(:, j) = Q(:, j) - Q(:, i - 1) * R(i - 1, j);
end
%% This multiply is slower than above
% Q(:, i : end) = ...
% Q(:, i : end) - ...
% Q(:, i - 1) * R(i - 1, i : end);
R(i, i) = norm(Q(:,i));
Q(:, i) = Q(:, i) ./ R(i, i);
end