如何向量化正常和點的陣列之間的點積之和

Question

我需要評估下面的表達式（僞算術符號）：

∑ipi⋅n

其中p是一個矩陣的三元向量和n是三元向量。我可以用for循環做如下，但我無法弄清楚如何 矢量化這樣的：

p = [1 1 1; 2 2 2]; 
n = [3 3 3]; 
s = 0; 
for i = 1:size(p, 1) 
    s = s + dot(p(i, :), n) 
end 

Answer 1

爲什麼複雜的事情？如何簡單的矩陣乘法：

s = sum(p * n(:)) 

其中p被假定爲中號逐3矩陣。

Answer 2

我認爲你可以bsxfun做到這一點：

sum(sum(bsxfun(@times,p,n))) 

Answer 3

---------- 


% Is it the same for this case? 


---------- 


n = 200;     % depending on the computer it might be 

m = 1000*n;    % that n needs to be chosen differently 

A = randn(n,m); 

x = randn(n,1); 

p = zeros(m,1); 

q = zeros(1,m); 
tic; 

for i = 1:m 

    p(i) = sum(x.*A(:,i)); 
    q(i) = sum(x.*A(:,i)); 
end 
time = toc; disp(['time = ',num2str(time)]);