获得与随机选择的特定浓度值相对应的多个 (x, y) 点

Question

我需要生成一个点矩阵，前提是它们满足在这些 (x,y) 点浓度大于 10 的条件。请注意，我首先运行一个代码让我浓度在每个位置 c(x,y,t)，现在根据第一个运行的结果，我需要 Matlab "randomly" 根据上述条件选择 (x,y) 点。另请注意第一个 Matlab 运行结果的维度（随机抽样应基于此）：浓度随位置和时间而变化，为 52x61x61，x 为 1x61，y 为 1x52，时间为 1x61 .

例如，对于值为 50 的随机选择的浓度，观察到该值的 x 和 y 是多少？我需要为 12 个不同的点做这个； c(x,y,t) 的 12 个不同值。

我希望我的问题有道理。谢谢。

Answer 1

如果我没有正确理解你的问题。这是一种蛮力方式来做你想做的事。希望能帮助到你。

% dimensions
N_X = 52;
N_Y = 61;
N_T = 61;
% space and time vectors
x = linspace(0,1,N_X);
y = linspace(0,1,N_Y);
t = linspace(0,1,N_T);
% set up a grid
[X Y T]         = meshgrid(y,x,t);
% init concentration as uniform random numbers in [0 100]
c_test      = rand(N_X,N_Y,N_T)*100;

% pick concentrations by some condition
condition   = c_test(:) > 99;
% count how many fulfill that condition
N_true      = sum(condition);

if N_true > 0
    % clear terminal for output
    clc
    % now prune the meshgrids and concentration matrices
    % so only the elements that fulfill the condition are true
    X_out = X(condition);
    Y_out = Y(condition);
    T_out = T(condition);
    C_out = c_test(condition);

    for i=1:12
        % pick one of the remaining elements
        % you may want to pick 12 unique elements ? 
        random_idx  = randi(N_true);
        % print to terminal 
        fprintf('c(%3.2f, %3.2f, %3.2f) = %3.1f\n', X_out(random_idx), Y_out(random_idx), T_out(random_idx), C_out(random_idx))
    end
end

我选择了高于 99% 以表明代码没有找到正确的元素纯属运气:)

这是输出：

c(0.80, 0.88, 0.47) = 99.4
c(0.30, 0.70, 0.65) = 100.0
c(0.10, 0.62, 0.23) = 99.2
c(0.58, 0.14, 0.37) = 99.1
c(0.25, 0.70, 0.98) = 99.5
c(0.20, 0.46, 0.08) = 99.2
c(0.07, 0.40, 0.05) = 99.5
c(0.05, 0.72, 0.82) = 99.8
c(0.10, 0.90, 0.65) = 99.3
c(0.93, 0.26, 0.22) = 99.5
c(0.05, 0.62, 0.12) = 99.6
c(0.85, 0.80, 0.87) = 99.2

Answer 2

嗯，既然你有坐标和力矩 x、y、t 和集中函数 c，计划是：

计算所有点的浓度；
找出高集中点在哪里；
计算那些高集中点的指数；
使用坐标和矩中的索引来获取位置。

代码应如下所示：

%// Dimensions:
%//   1st --> y
%//   2nd --> x
%//   3rd --> t
conc  = c(x,y,t);
high  = (conc > 50);
indx  = find(high);    

%// Here's the trick: convert back to subscripts the linear indices
%// of the random 12 positions/moments where the concentration was high.
select     = randi(numel(indx), 1, 12);
[yk,xk,tk] = ind2sub(size(high), indx(select));

%// Aggregate the results as (x,y,t) 3x12 numeric array
result = [x(xk); y(yk); t(tk)];

获得与随机选择的特定浓度值相对应的多个 (x, y) 点

Obtaining a number of (x, y) points that correspond to specific values of concentration that are chosen at random

random

3d

matlab

sample

conditional-statements