函数sum（）的matlab奇怪行为 [英] matlab strange behaviour of function sum()

问题描述

任何想法为什么Matlab可以表现得如此？

 >> sum（[0 0 0]）
下标索引必须是实数正整数或逻辑。 
 
>> sum（[1 1 1]）$ ​​b 
 $ b ans = 
 
 4 4 4 
  

与这2个多小时的战斗，仍然无法得到它。
这是我在这之前运行的代码。
在运行这段代码之前 - sum（）函数可以正常工作。

  price = 100; 
 vola = 0.2; 
 r = 0.05; 
 n_step = 3; 
 dt = 1/250; 
 S0 = 100; 
 T = 1; 
 
 s = [1 0 0 0; 1 2 0 0; 1 2 3 0; 1 2 3 4]; 
概率= 0.5; 
 n_path = 2 ^ n_step;二项式方法的瓶颈％b $ b avg_price = zeros（n_path，2）; ％第一列 - 概率，第二 - 平均价格
 path_matrix =零（n_path，n_step）; ％所有可能的路径1-up，0-down 
 for k = 0：n_path-1 
 path_matrix（k + 1，:) = de2bi（k，'left-msb'，n_step）; 
 end 
 
 node_matrix = path_matrix;对于k = 2，
：n_step 
 node_matrix（:, k）= node_matrix（:, k-1）+ node_matrix（:, k）; 
 end 
 node_matrix = node_matrix + 1; 
 
％遍历所有可能的路径并计算k = 1时的价格总和
：n_path 
％路径概率
 n_up = sum（path_matrix（k， ））; 
 avg_price（k，1）= prob ^ n_up *（1-prob）^（n_step-n_up）; 
 
％获得此路径上所有州的价格总和
 sum = s（1,1）; 
 for p = 1：n_step 
 sum = sum + s（p + 1，node_matrix（k，p））; 
 end 
 avg_price（k，2）= sum; 
 end 
  

解决方案

sum 现在它被认为是一个局部变量

  sum = s（ 1,1）; 
  

因此您是隐藏 sum 作为函数。

更改变量名称并执行

 明确总和
  

。

Any idea why Matlab could behave like this?

>> sum([0 0 0])
Subscript indices must either be real positive integers or logicals.

>> sum([1 1 1])

ans =

     4     4     4

Fighting with this more than 2 hours, still can't get it. This is the code I run before this happens. Before running this code - the function sum() works fine.

price = 100;
vola = 0.2;
r = 0.05;
n_step = 3;
dt = 1/250;
S0 = 100;
T = 1;

s = [1 0 0 0;1 2 0 0;1 2 3 0; 1 2 3 4];
prob = 0.5;
n_path = 2^n_step; % bottle neck for binomial approach
avg_price = zeros(n_path, 2); % first column - probability, second - average price
path_matrix = zeros(n_path, n_step); % all possible paths 1-up, 0-down
for k = 0:n_path-1
    path_matrix(k+1, :) = de2bi(k,'left-msb',n_step);
end

node_matrix = path_matrix;
for k=2:n_step
    node_matrix(:, k) = node_matrix(:, k-1) + node_matrix(:, k);
end
node_matrix = node_matrix + 1;

% go through all possible paths and calculate sum of prices
for k = 1:n_path
    % probability of path
    n_up = sum(path_matrix(k, :));
    avg_price(k, 1) = prob^n_up*(1 - prob)^(n_step - n_up);

    % get sum of prices over all states for this path
    sum = s(1, 1);
    for p = 1:n_step
        sum = sum + s(p+1, node_matrix(k, p));
    end
    avg_price(k, 2) = sum;
end

解决方案

you've overridden the function sum and now it is considered a local variable

 sum = s(1, 1);

thus you are hiding sum as function.

Change the variable name and do

 clear sum

.

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