Why is it doing all 100 attempts as a singular go?

Question

Larose 2024-5-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2120291-why-is-it-doing-all-100-attempts-as-a-singular-go

评论： Voss 2024-5-19

I am working on a bit of code to generate a the probability of an item dropping. I have it set so that its going through an if loop chain, where if it isnt one thing it goes to the next thing and if it isnt that it goes to the next and so forth, but when I try to run it with a for loop to dictate how many times it needs to run it just gives all of the attempts to a singular output giving that one output a probability of 100% each run, which isnt whats supposed to happen.

numOfSims = 100;
potionOfStrength = 0;
braceletOfStrength = 0;
hammerOfThunder = 0;
none = 0;
X = rand;
X2 = rand;
X3 = rand;
   
for iteration_num = 1:numOfSims
    if X<0.4
        potionOfStrength = potionOfStrength +1;
    else
        if X2<0.2
            braceletOfStrength = braceletOfStrength +1;
        else
            if X3<0.2
                hammerOfThunder = hammerOfThunder +1;
            else
                none = none +1;
            end
        end
    end

This is the code I've been working on.

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Answer 1

Voss 2024-5-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2120291-why-is-it-doing-all-100-attempts-as-a-singular-go#answer_1459806

编辑：Voss 2024-5-18

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Your code does the same thing 100 times because the random values don't change from one iteration to the next.

I guess you would want to generate new random X, X2, and X3 in each iteration of the for loop:

numOfSims = 100;
potionOfStrength = 0;
braceletOfStrength = 0;
hammerOfThunder = 0;
none = 0;
   
for iteration_num = 1:numOfSims
    
    X = rand;
    X2 = rand;
    X3 = rand;
    
    if X<0.4
        potionOfStrength = potionOfStrength +1;
    else
        if X2<0.2
            braceletOfStrength = braceletOfStrength +1;
        else
            if X3<0.2
                hammerOfThunder = hammerOfThunder +1;
            else
                none = none +1;
            end
        end
    end
    
end
potionOfStrength
potionOfStrength = 36
braceletOfStrength
braceletOfStrength = 16
hammerOfThunder
hammerOfThunder = 6
none
none = 42

Or make X, X2, and X3 random vectors of length numOfSims (i.e., 100), and index them inside the loop:

numOfSims = 100;
potionOfStrength = 0;
braceletOfStrength = 0;
hammerOfThunder = 0;
none = 0;
X = rand(1,numOfSims);
X2 = rand(1,numOfSims);
X3 = rand(1,numOfSims);
    
for iteration_num = 1:numOfSims
    
    if X(iteration_num)<0.4
        potionOfStrength = potionOfStrength +1;
    else
        if X2(iteration_num)<0.2
            braceletOfStrength = braceletOfStrength +1;
        else
            if X3(iteration_num)<0.2
                hammerOfThunder = hammerOfThunder +1;
            else
                none = none +1;
            end
        end
    end
    
end
potionOfStrength
potionOfStrength = 37
braceletOfStrength
braceletOfStrength = 13
hammerOfThunder
hammerOfThunder = 13
none
none = 37

In either case, you can utilize elseif to shorten your code, e.g.:

for iteration_num = 1:numOfSims
    X = rand;
    X2 = rand;
    X3 = rand;
    if X<0.4
        potionOfStrength = potionOfStrength +1;
    elseif X2<0.2
        braceletOfStrength = braceletOfStrength +1;
    elseif X3<0.2
        hammerOfThunder = hammerOfThunder +1;
    else
        none = none +1;
    end
end

or:

for iteration_num = 1:numOfSims
    if X(iteration_num)<0.4
        potionOfStrength = potionOfStrength +1;
    elseif X2(iteration_num)<0.2
        braceletOfStrength = braceletOfStrength +1;
    elseif X3(iteration_num)<0.2
        hammerOfThunder = hammerOfThunder +1;
    else
        none = none +1;
    end
end