我正在阅读优化工具箱的 Matlab 用户指南。第 1-15 页提供了一些用于创建索引变量的代码。这是代码:
%Combine variables into one vector
variables = {'I1','I2','HE1','HE2','LE1','LE2','C','BF1',...
'BF2','HPS','MPS','LPS','P1','P2','PP','EP'};
N = length(variables);
% create variables for indexing
for v = 1:N
eval([variables{v},' = ',num2str(v),';']); %?
end
我知道“变量”的类别是元胞数组。但我无法清楚地理解“eval”的功能。阅读下面的代码,它似乎为变量中的元素创建了索引,以便元素可以用作操作矩阵或向量的索引号。例如:
lb = zeros(size(variables));
lb([P1,P2,MPS,LPS]) = [2500,3000,271536,100623];
我已经阅读了帮助文档,但仍然无法获取。所以,任何人都可以为我解释得更清楚。
顺便说一句,用户指南建议避免使用此“eval”功能。那么,有没有其他方法可以实现上述功能呢?
谢谢大家
完整的程序
% Combine variables into one vector
variables = {'I1','I2','HE1','HE2','LE1','LE2','C','BF1',...
'BF2','HPS','MPS','LPS','P1','P2','PP','EP'};
N = length(variables);
% create variables for indexing
for v = 1:N
eval([variables{v},' = ',num2str(v),';']); %?
end
% Write bound constraints
lb = zeros(size(variables));
lb([P1,P2,MPS,LPS]) = ...
[2500,3000,271536,100623];
ub = Inf(size(variables));
ub([P1,P2,I1,I2,C,LE2]) = ...
[6250,9000,192000,244000,62000,142000];
% Write linear inequality constraints
A = zeros(3,N);
A(1,I1) = 1; A(1,HE1) = -1; b(1) = 132000;
A(2,EP) = -1; A(2,PP) = -1; b(2) = -12000;
A(3,[P1,P2,PP]) = [-1,-1,-1]; b(3) = -24550;
% Write linear equality constraints
Aeq = zeros(8,N); beq = zeros(8,1);
Aeq(1,[LE2,HE2,I2]) = [1,1,-1];
Aeq(2,[LE1,LE2,BF2,LPS]) = [1,1,1,-1];
Aeq(3,[I1,I2,BF1,HPS]) = [1,1,1,-1];
Aeq(4,[C,MPS,LPS,HPS]) = [1,1,1,-1];
Aeq(5,[LE1,HE1,C,I1]) = [1,1,1,-1];
Aeq(6,[HE1,HE2,BF1,BF2,MPS]) = [1,1,1,-1,-1];
Aeq(7,[HE1,LE1,C,P1,I1]) = [1267.8,1251.4,192,3413,-1359.8];
Aeq(8,[HE2,LE2,P2,I2]) = [1267.8,1251.4,3413,-1359.8];
% Write the objectvie
f = zeros(size(variables));
f([HPS PP EP]) = [0.002614 0.0239 0.009825];
% Solve the problem
%print out the results in floating-point fromat in a field 12 characters
%wide, including 2 digits after the decimal point for first data
[x,fval] = linprog(f,A,b,Aeq,beq,lb,ub);
for d = 1:N
fprintf('%12.2f \t %s \n',x(d),variables{d});
end
fval