I want to make random values that satisfies specific conditions. But I have a problem. help me please.

I want to make random values that satisfies (a+b<2) and (a+b>2).The range of 'a' is -1<a<0 and the range of 'b' is 2<b<3. But I have a problem. help me please. I tried to make random value of 'a' and 'b' and then find the combination of numbers but I can`t.

Below is the algorithm i made.

a = -1 + (1+0)*rand(10000,1);
b = 2 + (1+0)*rand(10000,1);

for i = 1:10000
    for j = 1:10000
        if a(i,1) + b(j,1) < 0
        c(i,1) = a(i,1);
        c(i,2) = b(j,2);
        end
    end
end

Answer 1

[Stephan]

Hi,

you generate numbers:

-1 < a < 0 and 2 < b < 3

your selection criterion for c is:

if a(i,1) + b(j,1) < 0

No combination of a+b will ever be < 0. All possible combinations of a+b will always be between 1 < (a+b) < 3.

That is why you get no values for c.

Change the condition in a way, that is satisfiable, then your code will run.

Here you have an example with the condition a+b < 2 (see comments for further information, there was an indexing error at line 9 also):

a = -1 + (1+0)*rand(10,1); % becareful with number of values
b = 2 + (1+0)*rand(10,1); % when you plan to combine them
d = 0; % counter for matrix c, its unknown yet how many values it gets
for i = 1:10
    for j = 1:10
        if a(i,1) + b(j,1) < 2
            d = d+1;
            c(d,1) = a(i,1);
            c(d,2) = b(j,1); %before: b(j,2) --> b has only 1 column
        end
    end
end