apply if-else-statement to a 3D matrix

Dear community,

Maybe this is a somewhat obvious question, but I have a 3D matrix with normally distributed simulations like the following:

n=10000
x1 = 75:125;
y1 = 0:40;
Qd=zeros(n,length(y1),length(x1));
for i = 1:length(x1) % mean
    for j = 1:length(y1) % sd
            Qd(:,i,j)=normrnd(x1(i),y1(j),n,1); 
    end           
end

Based on this matrix, I want to create another one with 3 conditionals. If the element Qd(k,i,j) is less than 25 then the new matrix should have a 50; if it is between 25 and 50 it should give me 10; if it is greater than 50 it should give me 30. The problem is that I have tried with the following and the elseif command is not working properly :( Any hint will be really appreciated! Thank you!

Pw=zeros(n,length(y1),length(x1));
for k = 1:n
    for i = 1:length(x1) 
        for j = 1:length(y1)
            if Q_d(k,i,j)<=25
                Pw(k,i,j)=50;
            elseif 25<Q_d(k,i,j)<=50
                Pw(k,i,j)=10;
            else
                Pw(k,i,j)=30; 
            end        
        end
    end
end

Answer 1

[Dyuman Joshi]

The syntax for comparing multiple conditions is individualistic in MATLAB, i.e. you have to write code for each condition individually -

elseif 25<Q_d(k,i,j) && Q_d(k,i,j)<=50

Edit - The pre-allocation of Pw w.r.t to the individual dimensions and the loop indices does not match

[Angelavtc]

Thank you very much @Dyuman Joshi ! I changed the condition and it works :) However, what do you mean with: "The pre-allocation of Pw w.r.t to the individual dimensions and the loop indices does not match"?

[Dyuman Joshi]

Pw=zeros(n,length(y1),length(x1));

You initialised Pw with dimensions corresponding to n, y1 and x1 respectively. However, in your loop

for k = 1:n
    for i = 1:length(x1) 
        for j = 1:length(y1)
            if Q_d(k,i,j)<=25

The respective loop variables correspond to n, x1 and y1. Which are not equal to n, y1 and x1 (order) as in the definition of Pw.

%Either you can change the order of indices
Q_d(k,j,i)
%or change the loop parameters.

I hope you get my point.

[Angelavtc]

Sure! thank you @Dyuman Joshi :)