Converting a 1x1 Vector into a Scalar Number

Question

Bianca Batista 2018-5-14

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https://ww2.mathworks.cn/matlabcentral/answers/400584-converting-a-1x1-vector-into-a-scalar-number

回答： Aakash Deep 2018-5-14

I have written the following code: number_trials=10000; number_generations=21;

 number_resistant_colonies_Darwin=zeros(number_trials,1);
 generation_number=zeros(number_trials,1);
 final_number_bacteria=150*2^21;
 alpha=1e-8;
 for j=1:number_trials 
    NWild=zeros(1,number_generations+1);
    NMutant=zeros(1,number_generations+1);
    NWild(1)=150; 
    NMutant(1)=0; 
    for i=1:number_generations 
        New_born_mutants=poissrnd(alpha*NWild(i)); 
        NWild(i+1)=(2*NWild(i))-New_born_mutants; 
        NMutant(i+1)=(2* NMutant(i))+New_born_mutants;  
    end
    number_resistant_colonies_Darwin(j)=NMutant(end);
    k=find(NMutant,1);
    generation_number(j)=k
 end

I keep receiving this error message: "Unable to perform assignment because the left and right sides have a different number of elements. Error in (line 22) generation_number(j)=k"

I understand that k is a 1x1 vector so it can't be entered into generation_number. How can I convert k into a scalar so that the number can be inputed into the generation_number matrix?

Thanks!

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Stephen23 2018-5-14

编辑：Stephen23 2018-5-14

"I understand that k is a 1x1 vector.... How can I convert k into a scalar..."

MATLAB does not have a data class named "scalar": a scalar is simply a 1x1x1x1x... array. Likewise a matrix is simply an RxCx1x1x1x1x... array. There are no special data types for these, their classification as scalar/vector/matrix/... depends solely upon their sizes, but does not change anything about the class/type of the object in memory. Learn more about basic MATLAB classes:

https://www.mathworks.com/help/matlab/matlab_prog/fundamental-matlab-classes.html

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Answer 1

Walter Roberson 2018-5-14

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In one of your runs, there are no non-zero entries in NMutant, so k is returning empty.

If you look at the examples in https://www.mathworks.com/help/stats/poissrnd.html you can see that poissrnd() can return entries that are 0.

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Answer 2

Aakash Deep 2018-5-14

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I agree with Stephen Cobeldick comments that there is no data class as scalar/vector/matrix, it all depends on their dimensions. The error you are getting is because the variable k is empty that's why it's giving an error of dimension mismatch. Try to correct the dimension of k and your code will work.